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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2018	Jul. 25, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	ARNC
Entity Registrant Name	Arconic Inc.
Entity Central Index Key	0000004281
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		482,954,718

Statement of Consolidated Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Sales (C & D)	$ 3,573	$ 3,261	$ 7,018	$ 6,453
Cost of goods sold (exclusive of expenses below)	2,903	2,549	5,671	5,007
Selling, general administrative, and other expenses	158	200	330	417
Research and development expenses	29	29	52	57
Provision for depreciation and amortization	144	137	286	270
Restructuring and other charges (E)	15	26	22	99
Operating income	324	320	657	603
Interest expense (N)	89	183	203	298
Other expense (income), net (F)	41	(132)	61	(448)
Income before income taxes	194	269	393	753
Provision for income taxes (H)	74	57	130	219
Net income	120	212	263	534
Amounts Attributable to Arconic Common Shareholders (I):
Net income	$ 120	$ 194	$ 262	$ 499
Earnings per share - basic (in usd per share)	$ 0.25	$ 0.44	$ 0.54	$ 1.13
Earnings per share - diluted (in usd per share)	0.24	0.43	0.53	1.07
Dividends paid per share (in usd per share)	$ 0.06	$ 0.06	$ 0.12	$ 0.12
Weighted Average Shares Outstanding (J):
Average shares outstanding - basic (in shares)	483	441	483	440
Average shares outstanding - diluted (in shares)	502	462	502	500

Statement of Consolidated Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income	$ 120	$ 212	$ 263	$ 534
Other comprehensive (loss) income, net of tax (J):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	29	48	172	79
Foreign currency translation adjustments	(201)	99	(79)	166
Net change in unrealized gains on available-for-sale securities	(2)	(101)	(2)	(134)
Net change in unrecognized losses/gains on cash flow hedges	4	(2)	(3)	3
Total Other comprehensive (loss) income, net of tax	(170)	44	88	114
Comprehensive (loss) income	(50)	256	351	648
Arconic
Net income	120	212	263	534
Other comprehensive (loss) income, net of tax (J):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	29	48	172	79
Foreign currency translation adjustments	(201)	99	(79)	166
Net change in unrealized gains on available-for-sale securities	(2)	(101)	(2)	(134)
Net change in unrecognized losses/gains on cash flow hedges	4	(2)	(3)	3
Total Other comprehensive (loss) income, net of tax	(170)	44	88	114
Comprehensive (loss) income	(50)	256	351	648
Noncontrolling Interests
Net income	0	0	0	0
Other comprehensive (loss) income, net of tax (J):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	0	0	0	0
Foreign currency translation adjustments	0	0	0	0
Net change in unrealized gains on available-for-sale securities	0	0	0	0
Net change in unrecognized losses/gains on cash flow hedges	0	0	0	0
Total Other comprehensive (loss) income, net of tax	0	0	0	0
Comprehensive (loss) income	$ 0	$ 0	$ 0	$ 0

Consolidated Balance Sheet (unaudited) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 1,455	$ 2,150
Receivables from customers, less allowances of $5 in 2018 and $8 in 2017 (K)	1,159	1,035
Other receivables (K)	478	339
Inventories (L)	2,659	2,480
Prepaid expenses and other current assets	324	374
Total current assets	6,075	6,378
Properties, plants, and equipment, net (M)	5,582	5,594
Goodwill (A & M)	4,518	4,535
Deferred income taxes	626	743
Intangibles, net	963	987
Other noncurrent assets	455	481
Total assets	18,219	18,718
Current liabilities:
Accounts payable, trade	2,024	1,839
Accrued compensation and retirement costs	364	399
Taxes, including income taxes	69	75
Accrued interest payable	113	124
Other current liabilities	362	349
Short-term debt	45	38
Total current liabilities	2,977	2,824
Long-term debt, less amount due within one year (N & O)	6,312	6,806
Accrued pension benefits (G)	2,184	2,564
Accrued other postretirement benefits	815	841
Other noncurrent liabilities and deferred credits	713	759
Total liabilities	13,001	13,794
Contingencies and commitments (Q)
Arconic shareholders’ equity:
Preferred stock	55	55
Common stock	483	481
Additional capital	8,295	8,266
Accumulated deficit	(1,073)	(1,248)
Accumulated other comprehensive loss (J)	(2,556)	(2,644)
Total Arconic shareholders’ equity	5,204	4,910
Noncontrolling interests	14	14
Total equity	5,218	4,924
Total liabilities and equity	$ 18,219	$ 18,718

Consolidated Balance Sheet (unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable, current	$ 5	$ 8

Statement of Consolidated Cash Flows (unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net income	$ 263	$ 534
Adjustments to reconcile net income to cash used for operations:
Depreciation and amortization	286	270
Deferred income taxes	47	27
Restructuring and other charges	22	99
Net loss (gain) from investing activities - asset sales (F)	5	(515)
Net periodic pension benefit cost (G)	71	108
Stock-based compensation	29	48
Other	50	115
Changes in assets and liabilities, excluding effects of acquisitions, divestitures, and foreign currency translation adjustments:
(Increase) in receivables (B)	(709)	(567)
(Increase) in inventories	(220)	(150)
Decrease in prepaid expenses and other current assets	8	30
Increase (decrease) in accounts payable, trade	218	(69)
(Decrease) in accrued expenses	(84)	(105)
Increase in taxes, including income taxes	37	121
Pension contributions	(237)	(163)
(Increase) in noncurrent assets	(4)	(60)
(Decrease) in noncurrent liabilities	(42)	(39)
Cash used for operations	(260)	(316)
Financing Activities
Net change in short-term borrowings (original maturities of three months or less)	5	9
Additions to debt (original maturities greater than three months)	300	512
Premiums paid on early redemption of debt (B & N)	(17)	(52)
Payments on debt (original maturities greater than three months) (N)	(801)	(1,333)
Proceeds from exercise of employee stock options	13	26
Dividends paid to shareholders	(60)	(88)
Distributions to noncontrolling interests	0	(14)
Other	(17)	(15)
Cash used for financing activities	(577)	(955)
Investing Activities
Capital expenditures	(288)	(229)
Proceeds from the sale of assets and businesses (P)	5	(9)
Sales of investments (F)	9	888
Cash receipts from sold receivables (B & K)	420	285
Other	0	244
Cash provided from investing activities	146	1,179
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(2)	4
Net change in cash, cash equivalents and restricted cash (B)	(693)	(88)
Cash, cash equivalents and restricted cash at beginning of year (B)	2,153	1,878
Cash, cash equivalents and restricted cash at end of period (B)	$ 1,460	$ 1,790

Statement of Changes in Consolidated Equity (unaudited) - USD ($) $ in Millions	Total	Preferred Class A	Preferred Class B	Preferred stock	Mandatory convertible preferred stock	Common stock	Additional capital	Accumulated deficit	Accumulated deficit Preferred Class A	Accumulated deficit Preferred Class B	Accumulated other comprehensive loss	Noncontrolling Interests
Balance at beginning of period at Dec. 31, 2016	$ 5,141			$ 55	$ 3	$ 438	$ 8,214	$ (1,027)			$ (2,568)	$ 26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	534							534				0
Other comprehensive income (loss) (J)	114										114	0
Cash dividends declared:
Preferred dividends declared, value		$ (1)	$ (34)						$ (1)	$ (34)
Common share, value	(54)							(54)
Stock-based compensation	48						48
Common stock issued: compensation plans	3					3
Distributions	(14)											(14)
Other	16							15				1
Balance at end of period at Jun. 30, 2017	5,753			55	3	441	8,262	(567)			(2,454)	13
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	212											0
Other comprehensive income (loss) (J)	44											0
Balance at end of period at Jun. 30, 2017	5,753			55	3	441	8,262	(567)			(2,454)	13
Balance at beginning of period at Dec. 31, 2017	4,924			55	0	481	8,266	(1,248)			(2,644)	14
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	263							263				0
Other comprehensive income (loss) (J)	88										88	0
Cash dividends declared:
Preferred dividends declared, value		$ (1)							$ (1)
Common share, value	(87)							(87)
Stock-based compensation	29						29
Common stock issued: compensation plans	2					2	0
Balance at end of period at Jun. 30, 2018	5,218			55	0	483	8,295	(1,073)			(2,556)	14
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	120											0
Other comprehensive income (loss) (J)	(170)											0
Balance at end of period at Jun. 30, 2018	$ 5,218			$ 55	$ 0	$ 483	$ 8,295	$ (1,073)			$ (2,556)	$ 14

Statement of Changes in Consolidated Equity (unaudited) (Parenthetical) - $ / shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Common stock, dividends per share (in usd per share)	$ 0.18	$ 0.12
Preferred Class A
Preferred, dividends per share (in usd per share)	1.875	1.875
Preferred Class B
Preferred, dividends per share (in usd per share)	$ 0	$ 13.4375

Basis of Presentation	6 Months Ended
Basis of Presentation	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The interim Consolidated Financial Statements of Arconic Inc. and its subsidiaries (“Arconic” or the “Company”) are unaudited. These Consolidated Financial Statements include all adjustments, consisting only of normal recurring adjustments, considered necessary by management to fairly state the Company’s results of operations, financial position, and cash flows. The results reported in these Consolidated Financial Statements are not necessarily indicative of the results that may be expected for the entire year. The 2017 year-end balance sheet data was derived from audited financial statements but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). This Form 10-Q report should be read in conjunction with Arconic’s Annual Report on Form 10-K for the year ended December 31, 2017, which includes all disclosures required by GAAP. Certain amounts in previously issued financial statements were reclassified to conform to the current period presentation (see below and Note D). On January 1, 2018, Arconic adopted new guidance issued by the Financial Accounting Standards Board (FASB) related to the following: presentation of net periodic pension cost and net periodic postretirement benefit cost that required a reclassification of costs within the Statement of Consolidated Operations; presentation of certain cash receipts and cash payments within the Statement of Consolidated Cash Flows that required a reclassification of amounts between operating and either financing or investing activities; and the classification of restricted cash within the statement of cash flows. See Note B for further details. In January 2018, management changed the organizational structure of the businesses in its Engineered Products and Solutions (EP&S) segment, from four business units to three business units, with a focus on aligning its internal structure to core markets and customers and reducing cost. As a result of this change in the EP&S segment organizational structure, management assessed and concluded that each of the three business units represent reporting units for goodwill impairment evaluation purposes. Also, as a result of the reorganization, goodwill was reallocated to the three new reporting units and evaluated for impairment during the first quarter of 2018. The estimated fair value of each reporting unit substantially exceeded its carrying value; thus, there was no goodwill impairment. More than 92% of Arconic’s total goodwill at March 31, 2018 was allocated to the following three EP&S reporting units: Arconic Engines ($2,095), Arconic Fastening Systems ($1,623) and Arconic Engineered Structures ($517). See Note M for further details of an interim goodwill impairment evaluation that was performed for the Arconic Engines reporting unit during the second quarter of 2018.

Recently Adopted and Recently Issued Accounting Guidance	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Recently Adopted and Recently Issued Accounting Guidance	Recently Adopted and Recently Issued Accounting Guidance Adopted In May 2014, the FASB issued changes to the recognition of revenue from contracts with customers. These changes created a comprehensive framework for all entities in all industries to apply in the determination of when to recognize revenue and, therefore, supersede virtually all existing revenue recognition requirements and guidance. This framework is expected to result in less complex guidance in application while providing a consistent and comparable methodology for revenue recognition. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, an entity should apply the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract(s), (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract(s), and (v) recognize revenue when, or as, the entity satisfies a performance obligation. These changes became effective for Arconic on January 1, 2018. Arconic adopted this new guidance using the modified retrospective transition approach applied to those contracts that were not completed as of January 1, 2018. There was no cumulative effect adjustment to the opening balance of retained earnings in the Consolidated Balance Sheet in the first quarter of 2018, as the adoption did not result in a change to our timing of revenue recognition, which continues to be at a point in time. See Note C for further details. In January 2016, the FASB issued changes to equity investments. These changes require equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. However, an entity may choose to measure equity investments that do not have readily determinable fair values using the measurement alternative of cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer. Also, the impairment assessment of equity investments without readily determinable fair values has been simplified by requiring a qualitative assessment to identify impairment. Also, the new guidance required changes in fair value of equity securities to be recognized immediately as a component of net income instead of being reported in accumulated other comprehensive loss until the gain (loss) is realized. These changes became effective for Arconic on January 1, 2018 and have been applied on a prospective basis. Arconic elected the measurement alternative for its equity investments that do not have readily determinable fair values. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements. In August 2016, the FASB issued changes to the classification of certain cash receipts and cash payments within the statement of cash flows. The guidance identifies eight specific cash flow items and the sections where they must be presented within the statement of cash flows. These changes became effective for Arconic on January 1, 2018 and have been be applied retrospectively. As of result of the adoption, Arconic reclassified cash received related to beneficial interest in previously transferred trade accounts receivables from operating activities to investing activities in the Statement of Consolidated Cash Flows. This new accounting standard does not reflect a change in our underlying business or activities. The reclassification of cash received related to beneficial interest in previously transferred trade accounts receivables was $285 for the six months ended June 30, 2017. In addition, Arconic reclassified $52 of cash paid for debt prepayments including extinguishment costs from operating activities to financing activities for the six months ended June 30, 2017. In November 2016, the FASB issued changes to the classification of cash and cash equivalents within the statement of cash flow. Restricted cash and cash equivalents will be included within the cash and cash equivalents line on the cash flow statement and a reconciliation must be prepared to the statement of financial position. Transfers between restricted cash and cash equivalents and cash and cash equivalents will no longer be presented as cash flow activities in the Statement of Consolidated Cash Flows and for material balances of restricted cash and restricted cash equivalents Arconic will disclose information regarding the nature of the restrictions. These changes became effective for Arconic on January 1, 2018 and have been applied retrospectively. Management has determined that the adoption of this guidance did not have a material impact on the Statement of Consolidated Cash Flows. Restricted cash was $5, $4 and $5 at June 30, 2018, December 31, 2017 and June 30, 2017, respectively. In March 2017, the FASB issued changes to the presentation of net periodic pension cost and net periodic postretirement benefit cost. The new guidance requires registrants to present the service cost component of net periodic benefit cost in the same income statement line item or items as other employee compensation costs arising from services rendered during the period. Also, only the service cost component will be eligible for asset capitalization. Registrants will present the other components of net periodic benefit cost separately from the service cost component; and, the line item or items used in the income statement to present the other components of net periodic benefit cost must be disclosed. These changes became effective for Arconic on January 1, 2018 and were adopted retrospectively for the presentation of the service cost component and the other components of net periodic benefit cost in the Statement of Consolidated Operations, and prospectively for the asset capitalization of the service cost component of net periodic benefit cost. The Company recorded the service related net periodic benefit cost within Cost of goods sold, Selling, general administrative, and other expenses and Research and development expenses and recorded the non-service related net periodic benefit cost (except for the curtailment cost which was recorded in Restructuring and other charges) separately from service cost in Other expense (income), net within the Statement of Consolidated Operations. The impact of the retrospective adoption of this guidance was an increase to consolidated Operating income of $39 and $77 while there was no impact to consolidated Net income for the second quarter or six months ended June 30, 2017, respectively. In May 2017, the FASB issued clarification to guidance on the modification accounting criteria for share-based payment awards. The new guidance requires registrants to apply modification accounting unless three specific criteria are met. The three criteria are 1) the fair value of the award is the same before and after the modification, 2) the vesting conditions are the same before and after the modification and 3) the classification as a debt or equity award is the same before and after the modification. These changes became effective for Arconic on January 1, 2018 and were applied prospectively to new awards modified after adoption. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements. Issued In February 2016, the FASB issued changes to the accounting and presentation of leases. These changes require lessees to recognize a right of use asset and lease liability on the balance sheet for all leases with terms longer than 12 months. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize a right of use asset and lease liability. Also, when measuring assets and liabilities arising from a lease, optional payments should be included only if the lessee is reasonably certain to exercise an option to extend the lease, exercise a purchase option, or not exercise an option to terminate the lease. As originally released, the standards update required application at the beginning of the earliest comparative period presented at the time of adoption. However, in July 2018, the FASB provided entities the option to instead apply the provisions of the new leases guidance at the effective date, without adjusting the comparative periods presented. These changes become effective for Arconic on January 1, 2019. Arconic’s current operating lease portfolio is primarily comprised of land and buildings, plant equipment, vehicles, and computer equipment. A cross-functional implementation team is in the process of determining the scope of arrangements that will be subject to this standard as well as assessing the impact to the Company’s systems, processes and internal controls. Arconic has contracted with a third-party vendor to implement a software solution. Concurrently, Arconic is compiling lease data to be uploaded into the software solution to account for leases under the new standard. Management is evaluating the impact of these changes on the Consolidated Balance Sheet, which will require right of use assets and lease liabilities be recorded for operating leases; therefore, an estimate of the impact is not currently determinable. However, the adoption is not expected to have a material impact on the Statement of Consolidated Operations or Statement of Consolidated Cash Flows. In June 2016, the FASB added a new impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses. The CECL model applies to most debt instruments, trade receivables, lease receivables, financial guarantee contracts, and other loan commitments. The CECL model does not have a minimum threshold for recognition of impairment losses and entities will need to measure expected credit losses on assets that have a low risk of loss. These changes become effective for Arconic on January 1, 2020. Management is currently evaluating the potential impact of these changes on the Consolidated Financial Statements. In August 2017, the FASB issued guidance that will make more financial and nonfinancial hedging strategies eligible for hedge accounting. It also amends the presentation and disclosure requirements and changes how companies assess effectiveness. It is intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. These changes become effective for Arconic on January 1, 2019. For cash flow and net investment hedges existing at the date of adoption, Arconic will apply a cumulative-effect adjustment related to eliminating the separate measurement of ineffectiveness to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year in which the amendment is adopted. The amended presentation and disclosure guidance is required only prospectively. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements. In February 2018, the FASB issued guidance that allows an optional reclassification from Accumulated other comprehensive loss to Accumulated deficit for stranded tax effects resulting from the Tax Cuts and Jobs Act enacted on December 22, 2017. These changes become effective for Arconic on January 1, 2019. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements.

Revenue from Contracts with Customers

6 Months Ended

Jun. 30, 2018

Revenue from Contract with Customer [Abstract]

Revenue from Contracts with Customers

The Company's contracts with customers are comprised of acknowledged purchase orders incorporating the Company’s standard terms and conditions, or for larger customers, terms under negotiated multi-year agreements. These contracts with customers typically consist of the manufacture of products which represent single performance obligations that are satisfied upon transfer of control of the product to the customer. The Company produces fastening systems; seamless rolled rings; investment castings, including airfoils and forged jet engine components; extruded, machined and formed aircraft parts; aluminum sheet and plate; integrated aluminum structural systems; architectural extrusions; and forged aluminum commercial vehicle wheels. Transfer of control is assessed based on alternative use of the products we produce and our enforceable right to payment for performance to date under the contract terms. Transfer of control and revenue recognition generally occur upon shipment or delivery of the product, which is when title, ownership and risk of loss pass to the customer and is based on the applicable shipping terms. The shipping terms vary across all businesses and depend on the product, the country of origin, and the type of transportation (truck, train, or vessel). An invoice for payment is issued at time of shipment. The Company’s objective is to have net 30-day terms. Our business units set commercial terms on which Arconic sells products to its customers. These terms are influenced by industry custom, market conditions, product line (specialty versus commodity products), and other considerations.

The following table disaggregates revenue by major end market served. Differences between segment totals and consolidated Arconic are in Corporate. In the second quarter and six months ended June 30, 2018, Corporate included $38 of costs related to settlements of certain customer claims primarily related to product introductions.



	Engineered Products and Solutions		Global Rolled Products		Transportation and Construction Solutions		Total Segment
Second quarter ended June 30, 2018
Aerospace	$	1,241	$	226	$	—	$	1,467
Transportation	119		612		253		984
Building and construction	—		60		297		357
Industrial and other	236		553		12		801
Total end-market revenue	$	1,596	$	1,451	$	562	$	3,609

Second quarter ended June 30, 2017
Aerospace	$	1,141	$	241	$	—	$	1,382
Transportation	97		475		200		772
Building and construction	—		51		283		334
Industrial and other	247		504		21		772
Total end-market revenue	$	1,485	$	1,271	$	504	$	3,260

Six months ended June 30, 2018
Aerospace	$	2,431	$	425	$	—	$	2,856
Transportation	216		1,210		496		1,922
Building and construction	—		108		582		690
Industrial and other	490		1,074		21		1,585
Total end-market revenue	$	3,137	$	2,817	$	1,099	$	7,053

Six months ended June 30, 2017
Aerospace	$	2,296	$	456	$	—	$	2,752
Transportation	190		968		373		1,531
Building and construction	—		100		545		645
Industrial and other	486		995		42		1,523
Total end-market revenue	$	2,972	$	2,519	$	960	$	6,451

Segment Information

6 Months Ended

Jun. 30, 2018

Segment Reporting [Abstract]

Segment Information

Arconic is a global leader in lightweight metals engineering and manufacturing. Arconic’s innovative, multi-material products, which include aluminum, titanium, and nickel, are used worldwide in aerospace, automotive, commercial transportation, building and construction, industrial applications, defense, and packaging. Arconic’s segments are organized by product on a worldwide basis. In the first quarter of 2018, the Company changed its primary measure of segment performance from Adjusted earnings before interest, tax, depreciation and amortization (“Adjusted EBITDA”) to Segment operating profit, which more closely aligns segment performance with Operating income as presented in the Statement of Consolidated Operations. Segment performance under Arconic’s management reporting system is evaluated based on a number of factors; however, the primary measure of performance is Segment operating profit. Arconic’s definition of Segment operating profit is Operating income excluding Special items. Special items include Restructuring and other charges and Impairment of goodwill. Segment operating profit also includes certain items that, under the previous segment performance measure, were recorded in Corporate, such as the impact of LIFO inventory accounting, metal price lag, intersegment profit eliminations, and derivative activities. Segment operating profit may not be comparable to similarly titled measures of other companies. Prior period financial information has been recast to conform to current year presentation. Differences between segment totals and consolidated Arconic are in Corporate.

The operating results of Arconic’s reportable segments were as follows:



	Engineered Products and Solutions		Global Rolled Products		Transportation and Construction Solutions		Total Segment
Second quarter ended June 30, 2018
Sales:
Third-party sales	$	1,596	$	1,451	$	562	$	3,609
Intersegment sales	—		46		—		46
Total sales	$	1,596	$	1,497	$	562	$	3,655
Profit and loss:
Segment operating profit	$	212	$	123	$	97	$	432
Restructuring and other charges	9		1		—		10
Provision for depreciation and amortization	70		53		12		135

Second quarter ended June 30, 2017
Sales:
Third-party sales	$	1,485	$	1,271	$	504	$	3,260
Intersegment sales	—		37		—		37
Total sales	$	1,485	$	1,308	$	504	$	3,297
Profit and loss:
Segment operating profit	$	250	$	133	$	71	$	454
Restructuring and other charges	8		17		6		31
Provision for depreciation and amortization	66		51		12		129



	Engineered Products and Solutions		Global Rolled Products		Transportation and Construction Solutions		Total Segment
Six months ended June 30, 2018
Sales:
Third-party sales	$	3,137	$	2,817	$	1,099	$	7,053
Intersegment sales	—		88		—		88
Total sales	$	3,137	$	2,905	$	1,099	$	7,141
Profit and loss:
Segment operating profit	$	433	$	235	$	164	$	832
Restructuring and other charges	10		—		—		10
Provision for depreciation and amortization	141		104		25		270

Six months ended June 30, 2017
Sales:
Third-party sales	$	2,972	$	2,519	$	960	$	6,451
Intersegment sales	—		71		—		71
Total sales	$	2,972	$	2,590	$	960	$	6,522
Profit and loss:
Segment operating profit	$	497	$	269	$	139	$	905
Restructuring and other charges	14		74		9		97
Provision for depreciation and amortization	130		101		24		255

The following table reconciles Total segment operating profit to Consolidated income before income taxes:



	Second quarter ended						Six months ended
	June 30,						June 30,
	2018			2017			2018			2017
Total segment operating profit	$	432		$	454		$	832		$	905
Unallocated amounts:
Restructuring and other charges	(15		)	(26		)	(22		)	(99		)
Corporate expense	(93		)	(108		)	(153		)	(203		)
Consolidated operating income	$	324		$	320		$	657		$	603
Interest expense	(89		)	(183		)	(203		)	(298		)
Other (expense) income, net	(41		)	132			(61		)	448
Consolidated income before income taxes	$	194		$	269		$	393		$	753

The total assets of Arconic's reportable segment were as follows:



	June 30, 2018		December 31, 2017
Engineered Products and Solutions	$	10,447	$	10,325
Global Rolled Products	4,153		3,955
Transportation and Construction Solutions	1,087		1,041
Total segment assets	$	15,687	$	15,321

The following table reconciles Total segment assets to Consolidated assets:



	June 30, 2018		December 31, 2017
Total segment assets	$	15,687	$	15,321
Unallocated amounts:
Cash and cash equivalents	1,455		2,150
Deferred income taxes	626		743
Corporate fixed assets, net	304		310
Fair value of derivative contracts	57		91
Other	90		103
Consolidated assets	$	18,219	$	18,718

Restructuring and Other Charges

6 Months Ended

Jun. 30, 2018

Restructuring and Related Activities [Abstract]

Restructuring and Other Charges

In the second quarter of 2018, Arconic recorded Restructuring and other charges of $15 ($12 after-tax), which included $9 ($7 after-tax) for pension curtailment charges; $4 ($3 after-tax) for layoff costs, including the separation of approximately 24 employees (all in the Engineered Products and Solutions segment); a charge of $5 ($4 after-tax) for exit costs primarily related to the New York office; a charge of $2 ($2 after-tax) for other miscellaneous items; and a benefit of $5 ($4 after-tax) for the reversal of a number of small layoff reserves related to prior periods.

In the six months ended June 30, 2018, Arconic recorded Restructuring and other charges of $22 ($17 after-tax), which included $14 ($11 after-tax) for pension curtailment charges; $8 ($6 after-tax) for layoff costs, including the separation of approximately 40 employees (24 in the Engineered Products and Solutions segment and 16 in Corporate); a charge of $5 ($4 after-tax) for exit costs primarily related to the New York office; a charge of $4 ($3 after-tax) for other miscellaneous items; and a benefit of $9 ($7 after-tax) for the reversal of a number of small layoff reserves related to prior periods.

In the second quarter of 2017, Arconic recorded Restructuring and other charges of $26 ($17 after-tax), which included $29 ($19 after-tax) for layoff costs related to cost reduction initiatives including the separation of approximately 352 employees (129 in the Engineered Products and Solutions segment, 110 in the Global Rolled Products segment, 93 in the Transportation and Construction Solutions segment, and 20 in Corporate); a net charge of $4 ($3 after-tax) for other miscellaneous items; a net benefit of $6 ($4 after-tax), for the reversal of forfeited executive stock compensation of $13, partially offset by a charge of $7 for the related severance; and a favorable benefit of $1 ($1 after-tax) for the reversal of a number of small layoff reserves related to prior periods.

In the six months ended June 30, 2017, Arconic recorded Restructuring and other charges of $99 ($86 after-tax), which included $48 ($32 after-tax) for layoff costs related to cost reduction initiatives including the separation of approximately 680 employees (243 in the Engineered Products and Solutions segment, 242 in the Global Rolled Products segment, 133 in the Transportation and Construction Solutions segment, and 62 in Corporate); a charge of $60 ($60 after-tax) related to the sale of the Fusina, Italy rolling mill; a net benefit of $6 ($4 after-tax), for the reversal of forfeited executive stock compensation of $13, partially offset by a charge of $7 for the related severance; a net benefit of $1 ($0 after-tax) for other miscellaneous items; and a favorable benefit of $2 ($2 after-tax) for the reversal of a number of small layoff reserves related to prior periods.

As of June 30, 2018, approximately 20 of the 40 employees associated with 2018 restructuring programs and approximately 530 of the 760 employees (previously 830) associated with 2017 restructuring programs (with planned departures in 2018) were separated; all of the separations associated with 2016 restructuring programs were essentially complete. Most of the remaining separations for the 2018 restructuring programs and all of the remaining separations for the 2017 restructuring programs, are expected to be completed by the end of 2018.

For the second quarter and six months ended June 30, 2018, cash payments of $2 and $3, respectively, were made against layoff reserves related to 2018 restructuring programs, cash payments of $8 and $23, respectively, were made against layoff reserves related to 2017 restructuring programs, and cash payments of $0 and $4, respectively, were made against the layoff reserves related to 2016 restructuring programs.

Activity and reserve balances for restructuring and other charges were as follows:



	Layoff costs			Other exit costs			Total
Reserve balances at December 31, 2016	$	50		$	9		$	59
Cash payments	(59		)	(6		)	(65		)
Restructuring charges	64			1			65
Other⁽¹⁾	1			(2		)	(1		)
Reserve balances at December 31, 2017	56			2			58
Cash payments	(30		)	—			(30		)
Restructuring charges	23			5			28
Other⁽¹⁾	(23		)	—			(23		)
Reserve balances at June 30, 2018	$	26		$	7		$	33


⁽¹⁾	Other includes reversals of previously recorded restructuring charges and the effects of foreign currency translation. In 2018, Other for layoff costs also included a reclassification of $14 in pension costs, as this liability was reflected in Arconic’s separate liability for pension obligations. In 2017, Other for layoff costs also included a reclassification of a stock awards reversal of $13.

The remaining reserves are expected to be paid in cash during 2018.

Other Expense (Income), Net

6 Months Ended

Jun. 30, 2018

Other Income and Expenses [Abstract]

Other Expense (Income), Net



	Second quarter ended						Six months ended
	June 30,						June 30,
	2018			2017			2018			2017
Non-service related net periodic benefit cost	$	28		$	39		$	56		$	77
Interest income	(4		)	(4		)	(10		)	(8		)
Foreign currency gains (losses), net	17			2			14			(3		)
Net loss (gain) from asset sales	2			(166		)	5			(515		)
Other, net	(2		)	(3		)	(4		)	1
	$	41		$	(132	)	$	61		$	(448	)

For the second quarter of 2017, Net loss (gain) from asset sales included a $167 gain on the debt-for-equity exchange with two investment banks (the “Investment Banks”) of the remaining portion of Arconic’s retained interest in Alcoa Corporation common stock for a portion of the Company’s outstanding notes held by the Investment Banks (the “Debt-for-Equity Exchange”). For the six months ended June 30, 2017, Net loss (gain) from asset sales included a gain on the sale of a portion of Arconic’s investment in Alcoa Corporation common stock of $351 that resulted in cash proceeds of $888 which were recorded in Sale of investments within Investing Activities in the Statement of Consolidated Cash Flows.

Pension and Other Postretirement Benefits

6 Months Ended

Jun. 30, 2018

Retirement Benefits [Abstract]

Pension and Other Postretirement Benefits

The components of net periodic benefit cost were as follows:



	Second quarter ended						Six months ended
	June 30,						June 30,
	2018			2017			2018			2017
Pension benefits
Service cost	$	8		$	21		$	28		$	44
Interest cost	55			58			110			116
Expected return on plan assets	(77		)	(82		)	(154		)	(165		)
Recognized net actuarial loss	42			55			84			110
Amortization of prior service cost (benefit)	1			2			2			3
Curtailments	9			—			14			—
Net periodic benefit cost⁽¹⁾	$	38		$	54		$	84		$	108

Other postretirement benefits
Service cost	$	2		$	2		$	4		$	4
Interest cost	7			7			14			15
Recognized net actuarial loss	2			1			4			2
Amortization of prior service cost (benefit)	(2		)	(2		)	(4		)	(4		)
Net periodic benefit cost⁽¹⁾	$	9		$	8		$	18		$	17


⁽¹⁾	Service cost was included within Cost of goods sold, Selling, general administrative, and other expenses, and Research and development expenses; curtailments were included in Restructuring and other charges; and all other cost components were recorded in Other expense (income), net in the Statement of Consolidated Operations.

In the first quarter of 2018, the Company announced that, effective April 1, 2018, benefit accruals for future service and compensation under all of the Company's qualified and non-qualified defined benefit pension plans for U.S. salaried and non-bargaining hourly employees ceased. As a result of this change, in the first quarter of 2018, the Company recorded a decrease to the accrued pension benefit liability of $136 related to the reduction of future benefits ($141 offset in Accumulated other comprehensive loss) and curtailment charges of $5 in Restructuring and other charges.

In conjunction with the separation of Alcoa Inc. on November 1, 2016, the Pension Benefit Guaranty Corporation approved management’s plan to separate the Alcoa Inc. pension plans between Arconic Inc. and Alcoa Corporation. The plan stipulates that Arconic will make cash contributions over a period of 30 months (from November 1, 2016) to its two largest pension plans. Payments are expected to be made in three increments of no less than $50 each ($150 total) over this 30-month period. The Company made payments of $50 in March 2018 and $50 in April 2017. Upon finalization of 2018 pension plan valuations, which are expected to be complete during the third quarter of 2018, additional cash contributions that were made in the first quarter of 2018 may be used to satisfy the $150 requirement.

On April 13, 2018, the United Auto Workers ratified a new five-year labor agreement, effective May 1, 2018, covering approximately 1,300 U.S. employees of Arconic. A provision within the agreement includes a retirement benefit increase for future retirees that participate in a defined benefit pension plan, which impacts approximately 300 of those employees. In addition, effective January 1, 2019, benefit accruals for future service will cease. As result of these changes, a curtailment charge of $9 was recorded in Restructuring and other charges in the second quarter of 2018.

Income Taxes

6 Months Ended

Jun. 30, 2018

Income Tax Disclosure [Abstract]

Income Taxes

Arconic’s year-to-date tax provision is comprised of the most recent estimated annual effective tax rate applied to year-to-date pre-tax ordinary income. The tax impact of unusual or infrequently occurring items, including changes in judgment about valuation allowances and effects of changes in tax laws or rates, are recorded discretely in the interim period in which they occur. In addition, the tax provision is adjusted for the interim period impact of non-benefited pre-tax losses.

For the six months ended June 30, 2018, the estimated annual effective tax rate, before discrete items, applied to ordinary income was 27.0%. This rate was higher than the federal statutory rate of 21%, which was enacted by the Tax Cuts and Jobs Act (the “2017 Act”) on December 22, 2017, primarily due to the additional estimated U.S. tax on Global Intangible Low-Taxed Income (GILTI) pursuant to the 2017 Act, domestic taxable income in certain U.S. states no longer subject to valuation allowance, and foreign income tax in higher rate jurisdictions.

For the six months ended June 30, 2017, the estimated annual effective tax rate, before discrete items, applied to ordinary income was 28.4%. This rate was lower than the federal statutory rate of 35% applicable to 2017 due to foreign income taxed in lower rate jurisdictions, a tax basis in excess of book basis in Alcoa Corporation common stock sold, and a nontaxable gain on the Debt-for-Equity Exchange. These beneficial items were partially offset by a loss on the sale of a rolling mill in Fusina, Italy for which no net tax benefit was recognized and valuation allowances related to U.S. foreign tax credits.

For the second quarter ended June 30, 2018 and June 30, 2017, the tax rate including discrete items was 38.1% and 21.2%, respectively. Discrete items of $21 were recorded in the second quarter ended June 30, 2018, primarily related to revised estimates of the provisional impact of the enactment of the 2017 Act discussed further below. There were no individually material discrete items recorded in the second quarter ended June 30, 2017.

The tax provisions for the second quarter and six months ended June 30, 2018 and 2017 were comprised of the following:



	Second quarter ended					Six months ended
	June 30,					June 30,
	2018		2017			2018		2017
Pre-tax income at estimated annual effective income tax rate before discrete items	$	52	$	60		$	106	$	214
Catch-up adjustment to revalue previous quarter pre-tax income at current estimated annual effective tax rate	1		—			—		—
Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized	—		(3		)	1		4
Other discrete items	21		—			23		1
Provision for income taxes	$	74	$	57		$	130	$	219

On December 22, 2017, the 2017 Act was signed into law, making significant changes to the Internal Revenue Code. Also on December 22, 2017, Staff Accounting Bulletin No. 118 ("SAB 118"), Income Tax Accounting Implications of the Tax Cuts and Jobs Act, was issued by the Securities and Exchange Commission to address the application of U.S. GAAP for financial reporting. SAB 118 permits the use of provisional amounts based on reasonable estimates in the financial statements. SAB 118 also provides that the tax impact may be considered incomplete in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the 2017 Act. Any adjustments to provisional or incomplete amounts should be included in income from continuing operations as an adjustment to tax expense or benefit in the reporting period that the amounts are determined within one year.

The Company's analysis of U.S. tax reform legislation, updated through June 30, 2018, resulted in an additional charge of $21 to the 2017 year-end provisional charge of $272. A charge of $18 was recorded for an increase in the provisional estimate of the one-time transition tax. An additional charge of $3 was also recorded for the portion of Alternative Minimum Tax ("AMT") credits expected to be refunded upon filing the 2018 tax return that will result in no benefit under government sequestration. The Company's estimates of the impact of the 2017 Act remain provisional through June 30, 2018.

The impact of the rate reduction will be finalized as part of the filing of the 2017 U.S. income tax return during 2018. Arconic will continue to analyze the amount of foreign earnings and profits, the associated foreign tax credits, and additional guidance that may be issued during 2018 in order to further update the estimated deemed repatriation calculation as necessary under SAB 118. Arconic has not yet gathered, prepared and analyzed all the necessary information in sufficient detail to determine whether any excess foreign tax credits that may result from the deemed repatriation will be realizable.

Provisional estimates of the impact of the 2017 Act on the realizability of certain deferred tax assets, including, but not limited to, foreign tax credits, AMT credits, and state tax loss carryforwards have been made based on information and computations that were available, prepared, and analyzed as of February 2, 2018. Through June 30, 2018, there were no changes to the estimates used to evaluate the realizability of deferred tax assets. Further analysis, or the issuance of additional guidance, could result in changes to the realizability of deferred tax assets.

As a result of the 2017 Act, the non-previously taxed post-1986 foreign earnings and profits (calculated based on U.S. tax principles) of certain U.S.-owned foreign corporations has been subject to U.S. tax under the one-time transition tax provisions. In the fourth quarter of 2017, Arconic had no plans to distribute such earnings in the foreseeable future and considered that conclusion to be incomplete under SAB 118. There is no change to this conclusion through June 30, 2018.

The 2017 Act creates a new requirement that certain income earned by foreign subsidiaries, GILTI, must be included in the gross income of the U.S. shareholder. The 2017 Act also established the Base Erosion and Anti-Abuse Tax (BEAT). Arconic anticipates that it will be subject to GILTI and has included an estimate of GILTI in the calculation of the 2018 estimated annual effective tax rate. At this time, Arconic does not anticipate being subject to BEAT for 2018. In the first quarter ended March 31, 2018, Arconic made a final accounting policy election to treat taxes due on future inclusions in U.S. taxable income related to GILTI as a current period expense when incurred.

In July 2018, the Company received notification from a foreign tax authority that their inquiry into the 2016 tax return was completed. The uncertain tax position taken on the tax return is effectively settled, and as a result, a previously unrecognized tax benefit of up to approximately $38 would be recognized in the third quarter of 2018 after evaluating the need for a valuation allowance.

Also in July 2018, Spain’s National Court upheld an assessment against the Company related to the 2006 through 2009 tax years. Arconic is preparing to petition the Supreme Court of Spain to review the National Court’s decision (see Note Q). As a result of the National Court’s decision, the Company will reassess its recognition and measurement of tax benefits related to the uncertain tax positions in the 2006 to 2009 tax years in the third quarter of 2018. The potential impact on the Provision for income taxes could be a charge of up to approximately $59 (€51) which would be recognized in the third quarter of 2018. As discussed in Note Q, under the Tax Matters Agreement, Alcoa Corporation is responsible for 49% of the net liability.

Earnings Per Share

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Earnings Per Share

Basic earnings per share (EPS) amounts are computed by dividing earnings, after the deduction of preferred stock dividends declared, by the average number of common shares outstanding. Diluted EPS amounts assume the issuance of common stock for all potentially dilutive share equivalents outstanding.

The information used to compute basic and diluted EPS attributable to Arconic common shareholders was as follows (shares in millions):



	Second quarter ended						Six months ended
	June 30,						June 30,
	2018		2017				2018			2017
Net income	$	120	$	212			$	263		$	534
Less: Preferred stock dividends declared	—		(18		)		(1		)	(35		)
Net income available to Arconic common shareholders - basic	120		194				262			499
Add: Interest expense related to convertible notes	3		2				6			4
Add: Dividends related to mandatory convertible preferred stock	—		—				—			34
Net income available to Arconic common shareholders - diluted	$	123	$	196		—	$	268		$	537

Average shares outstanding - basic	483		441				483			440
Effect of dilutive securities:
Stock options	—		2				—			2
Stock and performance awards	5		5				5			5
Mandatory convertible preferred stock	—		—				—			39
Convertible notes	14		14				14			14
Average shares outstanding - diluted	502		462				502			500

The following shares were excluded from the calculation of average shares outstanding – diluted as their effect was anti-dilutive (shares in millions).



	Second quarter ended		Six months ended
	June 30,		June 30,
	2018	2017	2018	2017
Mandatory convertible preferred stock	—	39	—	—
Stock options⁽¹⁾	9	7	9	7


⁽¹⁾	The average exercise price of options per share was $26.80 for the second quarter and six months ended June 30, 2018 and $28.85 for the second quarter and six months ended June 30, 2017.

Accumulated Other Comprehensive Loss

6 Months Ended

Jun. 30, 2018

Equity [Abstract]

Accumulated Other Comprehensive Loss

The following table details the activity of the four components that comprise Accumulated other comprehensive loss for both Arconic’s shareholders and noncontrolling interests:



	Arconic						Noncontrolling Interests
Second quarter ended June 30,	2018			2017			2018		2017
Pension and other postretirement benefits (G)
Balance at beginning of period	$	(2,087	)	$	(1,979	)	$	—	$	—
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	(15		)	17			—		—
Tax benefit (expense)	3			(5		)	—		—
Total Other comprehensive (loss) income before reclassifications, net of tax	(12		)	12			—		—
Amortization of net actuarial loss and prior service cost⁽¹⁾	52			56			—		—
Tax expense⁽²⁾	(11		)	(20		)	—		—
Total amount reclassified from Accumulated other comprehensive loss, net of tax⁽⁵⁾	41			36			—		—
Total Other comprehensive income	29			48			—		—
Balance at end of period	$	(2,058	)	$	(1,931	)	$	—	$	—
Foreign currency translation
Balance at beginning of period	$	(315	)	$	(622	)	$	—	$	(2	)
Other comprehensive (loss) income⁽³⁾	(201		)	99			—		—
Balance at end of period	$	(516	)	$	(523	)	$	—	$	(2	)
Available-for-sale securities
Balance at beginning of period	$	(2	)	$	99		$	—	$	—
Other comprehensive loss⁽⁴⁾	(2		)	(101		)	—		—
Balance at end of period	$	(4	)	$	(2	)	$	—	$	—
Cash flow hedges
Balance at beginning of period	$	18		$	4		$	—	$	—
Other comprehensive income (loss):
Net change from periodic revaluations	9			(4		)	—		—
Tax (expense) benefit	(1		)	1			—		—
Total Other comprehensive income (loss) before reclassifications, net of tax	8			(3		)	—		—
Net amount reclassified to earnings	(4		)	1			—		—
Tax benefit⁽²⁾	—			—			—		—
Total amount reclassified from Accumulated other comprehensive loss, net of tax⁽⁵⁾	(4		)	1			—		—
Total Other comprehensive income (loss)	4			(2		)	—		—
Balance at end of period	$	22		$	2		$	—	$	—

Total balance at end of period	$	(2,556	)	$	(2,454	)	$	—	$	(2	)


⁽¹⁾	These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note G).


⁽²⁾	These amounts were included in Provision for income taxes on the accompanying Statement of Consolidated Operations.


⁽³⁾	In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings.


⁽⁴⁾	Realized gains and losses were included in Other expense (income), net on the accompanying Statement of Consolidated Operations.


⁽⁵⁾	A positive amount indicates a corresponding charge to earnings and a negative amount indicates a corresponding benefit to earnings.



	Arconic						Noncontrolling Interests
Six months ended June 30,	2018			2017			2018		2017
Pension and other postretirement benefits (G)
Balance at beginning of period	$	(2,230	)	$	(2,010	)	$	—	$	—
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	122			11			—		—
Tax expense	(28		)	(4		)	—		—
Total Other comprehensive income before reclassifications, net of tax	94			7			—		—
Amortization of net actuarial loss and prior service cost⁽¹⁾	100			111			—		—
Tax expense⁽²⁾	(22		)	(39		)	—		—
Total amount reclassified from Accumulated other comprehensive loss, net of tax⁽⁵⁾	78			72			—		—
Total Other comprehensive income	172			79			—		—
Balance at end of period	$	(2,058	)	$	(1,931	)	$	—	$	—
Foreign currency translation
Balance at beginning of period	$	(437	)	$	(689	)	$	—	$	(2	)
Other comprehensive (loss) income⁽³⁾	(79		)	166			—		—
Balance at end of period	$	(516	)	$	(523	)	$	—	$	(2	)
Available-for-sale securities
Balance at beginning of period	$	(2	)	$	132		$	—	$	—
Other comprehensive loss⁽⁴⁾	(2		)	(134		)	—		—
Balance at end of period	$	(4	)	$	(2	)	$	—	$	—
Cash flow hedges
Balance at beginning of period	$	25		$	(1	)	$	—	$	—
Other comprehensive (loss) income:
Net change from periodic revaluations	3			4			—		—
Tax expense	—			(2		)	—		—
Total Other comprehensive income before reclassifications, net of tax	3			2			—		—
Net amount reclassified to earnings	(7		)	1			—		—
Tax benefit⁽²⁾	1			—			—		—
Total amount reclassified from Accumulated other comprehensive loss, net of tax⁽⁵⁾	(6		)	1			—		—
Total Other comprehensive (loss) income	(3		)	3			—		—
Balance at end of period	$	22		$	2		$	—	$	—

Total balance at end of period	$	(2,556	)	$	(2,454	)	$	—	$	(2	)


⁽¹⁾	These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note G).


⁽²⁾	These amounts were included in Provision for income taxes on the accompanying Statement of Consolidated Operations.


⁽³⁾	In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings.


⁽⁴⁾	Realized gains and losses were included in Other expense (income), net on the accompanying Statement of Consolidated Operations.


⁽⁵⁾	A positive amount indicates a corresponding charge to earnings and a negative amount indicates a corresponding benefit to earnings.

Receivables	6 Months Ended
Receivables	Jun. 30, 2018
Receivables [Abstract]
Receivables	Receivables Arconic has an arrangement with three financial institutions to sell certain customer receivables without recourse on a revolving basis. The sale of such receivables is completed using a bankruptcy remote special purpose entity, which is a consolidated subsidiary of Arconic. This arrangement provides for minimum funding of $200 up to a maximum of $400 for receivables sold. Arconic maintains a beneficial interest, or a right to collect cash, on the sold receivables that have not been funded (deferred purchase program). On March 30, 2012, Arconic initially sold $304 of customer receivables in exchange for $50 in cash and $254 of deferred purchase program under the arrangement. Arconic has received additional net cash funding of $300 ($2,658 in draws and $2,358 in repayments) since the program’s inception, including net cash draws totaling $0 ($300 in draws and $300 in repayments) for the six months ended June 30, 2018. As of June 30, 2018 and December 31, 2017, the deferred purchase program receivable was $313 and $187, respectively, which was included in Other receivables on the accompanying Consolidated Balance Sheet. The deferred purchase program receivable is reduced as collections of the underlying receivables occur; however, as this is a revolving program, the sale of new receivables will result in an increase in the deferred purchase program receivable. The gross amount of receivables sold and total cash collected under this program since its inception was $38,547 and $37,885, respectively. Arconic services the customer receivables for the financial institutions at market rates; therefore, no servicing asset or liability was recorded. Cash receipts from customer payments on sold receivables (which are cash receipts on the underlying trade receivables that have been previously sold in this program) as well as cash receipts and cash disbursements from draws and repayments under the program are presented as cash receipts from sold receivables within investing activities in the Statement of Consolidated Cash Flows.

Inventories

6 Months Ended

Jun. 30, 2018

Inventory Disclosure [Abstract]

Inventories



	June 30, 2018		December 31, 2017
Finished goods	$	682	$	669
Work-in-process	1,485		1,349
Purchased raw materials	401		381
Operating supplies	91		81
Total inventories	$	2,659	$	2,480

At June 30, 2018 and December 31, 2017, the portion of inventories valued on a last-in, first-out (LIFO) basis was $1,372 and $1,208, respectively. If valued on an average-cost basis, total inventories would have been $527 and $481 higher at June 30, 2018 and December 31, 2017, respectively.

In the second quarter of 2018, a charge of $23 was recorded in Cost of goods sold and Inventories to reflect a physical inventory adjustment at one plant in the EP&S segment. While a portion of this charge relates to prior years, the majority relates to 2018. The out-of-period amounts are not material to any interim or annual periods.

Property, Plants, and Equipment, Net

6 Months Ended

Jun. 30, 2018

Property, Plant and Equipment [Abstract]

Properties, Plants, and Equipment, Net



	June 30, 2018		December 31, 2017
Land and land rights	$	139	$	140
Structures	2,376		2,395
Machinery and equipment	9,148		8,830
	11,663		11,365
Less: accumulated depreciation and amortization	6,674		6,392
	4,989		4,973
Construction work-in-progress	593		621
	$	5,582	$	5,594

During the second quarter of 2018, the Company updated its three-year strategic plan and determined that there was a decline in the forecasted financial performance for the disks operations, an asset group within the Arconic Engines business unit. As such, the Company evaluated the recoverability of the long-lived assets by comparing their carrying value of approximately $515 to the estimated undiscounted net cash flows of the disk operations, resulting in an estimated fair value in excess of their carrying value of approximately 13%; thus, there was no impairment. If the disks operations do not achieve the revised forecasted financial performance or if there are changes in any significant assumptions, a material non-cash impairment of long-lived assets may occur in future periods. These significant assumptions include sales growth, cost of raw materials, ramp up of additional production capacity, and working capital. A 1% decrease in the forecasted net cash flows would reduce the undiscounted cash flows by approximately $6. The Company also performed an interim impairment evaluation of goodwill for the Arconic Engines reporting unit as a result of the decline in the forecasted performance of the disks operations during the second quarter of 2018. The estimated fair value of the reporting unit was substantially in excess of the carrying value; thus, there was no impairment of goodwill.

Debt

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Debt



	June 30, 2018			December 31, 2017
5.72% Notes, due 2019	$	—		$	500
1.63% Convertible Notes, due 2019	403			403
6.150% Notes, due 2020	1,000			1,000
5.40% Notes due 2021	1,250			1,250
5.87% Notes, due 2022	627			627
5.125% Notes, due 2024	1,250			1,250
5.90% Notes, due 2027	625			625
6.75% Bonds, due 2028	300			300
5.95% Notes, due 2037	625			625
Iowa Finance Authority Loan, due 2042	250			250
Other⁽¹⁾	(15		)	(23		)
Total debt	6,315			6,807
Less: amount due within one year	3			1
Total long-term debt	$	6,312		$	6,806


⁽¹⁾	Includes various financing arrangements related to subsidiaries, unamortized debt discounts related to outstanding notes and bonds listed in the table above, an equity option related to the convertible notes due in 2019, and unamortized debt issuance costs.

Public Debt – During the first quarter of 2018, the Company completed the early redemption of its remaining outstanding 5.72% Notes due in 2019, with aggregate principal amount of $500, for $518 in cash including accrued and unpaid interest. As a result, the Company recorded a charge of $19 in Interest expense in the accompanying Statement of Consolidated Operations for the first quarter of 2018 primarily for the premium paid on the early redemption of these notes in excess of their carrying value.

Credit Facilities. On July 25, 2014, Arconic entered into a Five-Year Revolving Credit Agreement with a syndicate of lenders and issuers named therein, which provides for a senior unsecured revolving credit facility (the “Credit Facility”). By an Extension Request and Amendment Letter dated as of June 5, 2015, the maturity date of the Credit Facility was extended to July 25, 2020. On September 16, 2016, Arconic entered into Amendment No. 1 to the Five-Year Revolving Credit Agreement to permit the Separation Transaction and to amend certain terms of the Credit Agreement, including the replacement of the existing financial covenant with a leverage ratio and reduction of total commitments available from $4,000 to $3,000. On June 29, 2018, Arconic entered into Amendment No. 2 (“Amendment No. 2”) to amend and restate the Five-Year Revolving Credit Agreement. The Five-Year Revolving Credit Agreement, as so amended and restated, is herein referred to as the “Credit Agreement.”

The Credit Agreement provides a $3,000 Credit Facility, the proceeds of which are to be used to provide working capital or for other general corporate purposes of Arconic. Subject to the terms and conditions of the Credit Agreement, Arconic may from time to time request increases in lender commitments under the Credit Facility, not to exceed $500 in aggregate principal amount, and may also request the issuance of letters of credit, subject to a letter of credit sublimit of $1,000 of the Credit Facility. Pursuant to the Credit Agreement, Arconic shall not permit the ratio of Consolidated Net Debt to Consolidated EBITDA (each as defined in the Credit Agreement) as of the end of each fiscal quarter for the period of the four fiscal quarters most recently ended, to be greater than 4.50 to 1.00, which maximum level will step down successively to 4.00 to 1.00 on December 31, 2018, and to 3.50 to 1.00 on December 31, 2019 and thereafter.

The Credit Agreement includes additional covenants, including, among others, (a) limitations on Arconic’s ability to incur liens securing indebtedness for borrowed money, (b) limitations on Arconic’s ability to consummate a merger, consolidation or sale of all or substantially all of its assets, and (c) limitations on Arconic’s ability to change the nature of its business. As of June 30, 2018, Arconic was in compliance with all such covenants.

The Credit Facility matures on June 29, 2023, unless extended or earlier terminated in accordance with the provisions of the Credit Agreement. Arconic may make two one-year extension requests during the term of the Credit Facility, subject to the lender consent requirements set forth in the Credit Agreement. Under the provisions of the Credit Agreement, Arconic will pay a fee of 0.25% per annum (based on Arconic’s long-term debt ratings as of June 30, 2018) of the total commitment to maintain the Credit Facility.

The Credit Facility is unsecured and amounts payable under it will rank pari passu with all other unsecured, unsubordinated indebtedness of Arconic. Borrowings under the Credit Facility may be denominated in U.S. dollars or euros. Loans will bear interest at a base rate or a rate equal to LIBOR, plus, in each case, an applicable margin based on the credit ratings of Arconic’s outstanding senior unsecured long-term debt. The applicable margin on base rate loans and LIBOR loans will be 0.50% and 1.50% per annum, respectively, based on Arconic’s long-term debt ratings as of June 30, 2018. Loans may be prepaid without premium or penalty, subject to customary breakage costs.

The obligation of Arconic to pay amounts outstanding under the Credit Facility may be accelerated upon the occurrence of an “Event of Default” as defined in the Credit Agreement. Such Events of Default include, among others, (a) non-payment of obligations; (b) breach of any representation or warranty in any material respect; (c) non-performance of covenants and obligations; (d) with respect to other indebtedness in a principal amount in excess of $100 million, a default thereunder that causes such indebtedness to become due prior to its stated maturity or a default in the payment at maturity of any principal of such indebtedness; (e) the bankruptcy or insolvency of Arconic; and (f) a change in control of Arconic.

There were no amounts outstanding at June 30, 2018 or December 31, 2017, and no amounts were borrowed during 2018 or 2017 under the Credit Facility.

In addition to the Credit Agreement above, Arconic has a number of other credit agreements that provide a combined borrowing capacity of $715 as of June 30, 2018, of which $350 is due to expire in 2018 and $365 is due to expire in 2019. The purpose of any borrowings under these credit arrangements is to provide for working capital requirements and for other general corporate purposes. The covenants contained in all these arrangements are the same as the Credit Agreement. During the six months ended June 30, 2018, Arconic borrowed and repaid $300 and $300, respectively, under these other credit facilities. The weighted-average interest rate and weighted-average days outstanding during the second quarter and six months ended June 30, 2018 were 3.3% and 70 days and 3.2% and 65 days, respectively.

Fair Value of Financial Instruments

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

The carrying values of Cash and cash equivalents, Restricted cash, Derivatives, Noncurrent receivables and Short-term debt included in the Consolidated Balance Sheet approximate fair values. The Company holds exchange-traded fixed income securities which are considered available-for-sale securities which are carried at fair value which is based on quoted market prices.

The following table summarizes Arconic’s financial liabilities that were not carried at fair value at June 30, 2018 and December 31, 2017:



	June 30, 2018				December 31, 2017
	Carrying value		Fair value		Carrying value		Fair value
Long-term debt, less amount due within one year	$	6,312	$	6,457	$	6,806	$	7,443

The fair value of Long-term debt, less amount due within one year was based on quoted market prices for public debt and on interest rates that are currently available to Arconic for issuance of debt with similar terms and maturities for non-public debt. The fair value amounts for all Long-term debt were classified in Level 2 of the fair value hierarchy.

Acquisitions and Divestitures	6 Months Ended
Acquisitions and Divestitures	Jun. 30, 2018
Business Combinations [Abstract]
Acquisitions and Divestitures	Acquisitions and Divestitures In March 2017, Arconic completed the sale of its Fusina, Italy rolling mill to Slim Aluminium. While owned by Arconic, the operating results and assets and liabilities of the Fusina, Italy rolling mill were included in the Global Rolled Products segment. As part of the transaction, Arconic injected $10 of cash into the business and provided a third-party guarantee with a fair value of $5 related to Slim Aluminium’s environmental remediation. The Company recorded a loss on the sale of $60, which was recorded in Restructuring and other charges (see Note E) on the Statement of Consolidated Operations in the first quarter of 2017. The rolling mill generated third-party sales of approximately $37 in the first quarter of 2017. At the time of the divestiture, the rolling mill had approximately 312 employees. On April 2, 2018, Arconic completed the sale of its Latin America extrusions business to a subsidiary of Hydro Extruded Solutions AS for $5 in cash, subject to post-closing adjustments that are not expected to be significant. The sales price approximates the carrying value of the net assets sold on the closing date, following the charge of $41 recognized in the fourth quarter of 2017 related to the non-cash impairment of the net book value of the business. The operating results and assets and liabilities of the business were included in the Transportation and Construction Solutions segment. This business generated sales of approximately $30 in the second quarter of 2017, and $25 and $56 in the six months ended June 30, 2018 and 2017, respectively.

Contingencies and Commitments	6 Months Ended
Contingencies and Commitments	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Commitments	Contingencies and Commitments Contingencies Environmental Matters Arconic participates in environmental assessments and cleanups at more than 100 locations. These include owned or operating facilities and adjoining properties, previously owned or operating facilities and adjoining properties, and waste sites, including Superfund (Comprehensive Environmental Response, Compensation and Liability Act (CERCLA)) sites. A liability is recorded for environmental remediation when a cleanup program becomes probable and the costs can be reasonably estimated. As assessments and cleanups proceed, the liability is adjusted based on progress made in determining the extent of remedial actions and related costs. The liability can change substantially due to factors such as the nature and extent of contamination, changes in remedial requirements, and technological changes, among others. Arconic’s remediation reserve balance was $287 at June 30, 2018 and $294 at December 31, 2017 (of which $51 and $41, respectively, was classified as a current liability), and reflects the most probable costs to remediate identified environmental conditions for which costs can be reasonably estimated. Payments related to remediation expenses applied against the reserve were $5 and $8 in the second quarter and six months ended June 30, 2018, respectively. This amount includes expenditures currently mandated, as well as those not required by any regulatory authority or third party. Included in annual operating expenses are the recurring costs of managing hazardous substances and environmental programs. These costs are estimated to be approximately 1% or less of cost of goods sold. The following discussion provides details regarding the current status of the most significant remediation reserves related to a current Arconic site. Massena West, NY—Arconic has an ongoing remediation project related to the Grasse River, which is adjacent to Arconic’s Massena plant site. Many years ago, it was determined that sediments and fish in the river contain varying levels of polychlorinated biphenyls (PCBs). The project, which was selected by the U.S. Environmental Protection Agency (EPA) in a Record of Decision issued in April 2013, is aimed at capping PCB contaminated sediments with concentration in excess of one part per million in the main channel of the river and dredging PCB contaminated sediments in the near-shore areas where total PCBs exceed one part per million. At June 30, 2018 and December 31, 2017, the reserve balance associated with this matter was $211 and $215, respectively. Arconic is in the planning and design phase of the project, which is expected to be completed in 2018. Following the submittal of the final design and EPA approval, the actual remediation fieldwork is expected to commence and take approximately four years. The majority of the project funding is expected to be incurred between 2018 and 2022. Tax Pursuant to the Tax Matters Agreement entered into between Arconic and Alcoa Corporation in connection with the separation transaction with Alcoa Corporation, Arconic shares responsibility with Alcoa Corporation, and Alcoa Corporation has agreed to partially indemnify Arconic for 49% of the ultimate liability, with respect to the following matter. As previously reported, in July 2013, following a Spanish corporate income tax audit covering the 2006 through 2009 tax years, an assessment was received mainly disallowing certain interest deductions claimed by a Spanish consolidated tax group owned by the Company. The assessment was $151 (€131), including interest. In August 2013, the Company filed an appeal of this assessment in Spain’s Central Tax Administrative Court, which was denied in January 2015. Arconic filed another appeal in Spain’s National Court in March 2015 which was denied in July 2018. The Company is preparing to petition the Supreme Court of Spain to review the National Court’s decision. If the petition is accepted, the Supreme Court will review the assessment on its merits and render a final decision. The National Court’s decision requires the assessment for the 2006 through 2009 tax years to be reissued to take into account the outcome of the 2003 to 2005 audit which was closed in 2017. The Company estimates the revised assessment to be $175 (€152), including interest. In the event the Company is unsuccessful in appealing the assessment to the Supreme Court of Spain, a portion of the assessment may be offset with existing net operating losses and tax credits available to the Spanish consolidated tax group, which would be shared between the Company and Alcoa Corporation as provided for in the Tax Matters Agreement. The Company will reassess the recognition and measurement of tax benefits related to the uncertain tax positions in the 2006 to 2009 tax years in the third quarter of 2018. The potential impact of the revised assessment on the Provision for income taxes could be a charge of up to approximately $59 (€51) which would be recognized in the third quarter of 2018. As stated above, Alcoa Corporation is responsible for 49% of the net liability. Additionally, while the tax years 2010 through 2013 are closed to audit, it is possible that the Company may receive assessments for tax years subsequent to 2013. Any potential assessment for an individual tax year is not expected to be material to the Company’s consolidated operations. Reynobond PE Howard v. Arconic Inc. et al. As previously reported, a purported class action complaint related to the Grenfell Tower fire was filed on August 11, 2017 in the United States District Court for the Western District of Pennsylvania against Arconic Inc. and Klaus Kleinfeld. A related purported class action complaint was filed in the United States District Court for the Western District of Pennsylvania on August 25, 2017, under the caption Sullivan v. Arconic Inc. et al., against Arconic Inc., two former Arconic executives, several current and former Arconic directors, and banks that acted as underwriters for Arconic’s September 18, 2014 preferred stock offering (the “Preferred Offering”). The plaintiff in Sullivan had previously filed a purported class action against the same defendants on July 18, 2017 in the Southern District of New York and, on August 25, 2017, voluntarily dismissed that action without prejudice. On February 7, 2018, on motion from certain putative class members, the court consolidated Howard and Sullivan, closed Sullivan, and appointed lead plaintiffs in the consolidated case. On April 9, 2018, the lead plaintiffs in the consolidated purported class action filed a consolidated amended complaint. The consolidated amended complaint alleges that the registration statement for the Preferred Offering contained false and misleading statements and omitted to state material information, including by allegedly failing to disclose material uncertainties and trends resulting from sales of Reynobond PE for unsafe uses and by allegedly expressing a belief that appropriate risk management and compliance programs had been adopted while concealing the risks posed by Reynobond PE sales. The consolidated amended complaint also alleges that between November 4, 2013 and June 23, 2017 Arconic and Kleinfeld made false and misleading statements and failed to disclose material information about the Company’s commitment to safety, business and financial prospects, and the risks of the Reynobond PE product, including in Arconic’s Form 10-Ks for the fiscal years ended December 31, 2013, 2014, 2015 and 2016, its Form 10-Qs and quarterly financial press releases from the fourth quarter of 2013 through the first quarter of 2017, its 2013, 2014, 2015 and 2016 Annual Reports, and its 2016 Annual Highlights Report. The consolidated amended complaint seeks, among other things, unspecified compensatory damages and an award of attorney and expert fees and expenses. On June 8, 2018, all defendants moved to dismiss the consolidated amended complaint for failure to state a claim. Briefing on that motion remains ongoing. Raul v. Albaugh, et al. On June 22, 2018, a derivative complaint was filed nominally on behalf of Arconic by a purported Arconic shareholder against all current members of Arconic’s Board of Directors, Klaus Kleinfeld and Ken Giacobbe, naming Arconic as a nominal defendant, in the United States District Court for the District of Delaware. The complaint raises similar allegations as the consolidated amended complaint in Howard, as well as allegations that the defendants improperly authorized the sale of Reynobond PE for unsafe uses, and asserts claims under Section 14(a) of the Securities Exchange Act of 1934 and Delaware state law. On July 13, 2018, the parties filed a stipulation agreeing to stay this case until the final resolution of the Howard case, the Grenfell Tower public inquiry in London, and the investigation by the London Metropolitan Police Service and on June 23, 2018, the Court approved the stay. While the Company believes that these cases are without merit and intends to challenge them vigorously, there can be no assurances regarding the ultimate resolution of these matters. Given the preliminary nature of these matters and the uncertainty of litigation, the Company cannot reasonably estimate at this time the likelihood of an unfavorable outcome or the possible loss or range of losses in the event of an unfavorable outcome. The Board of Directors has also received letters, purportedly sent on behalf of shareholders, reciting allegations similar to those made in the federal court lawsuits and demanding that the Board authorize the Company to initiate litigation against members of management, the Board and others. The Board of Directors has appointed a Special Litigation Committee of the Board to review and make recommendations to the Board regarding the appropriate course of action with respect to these shareholder demand letters. The Special Litigation Committee and the Board are continuing to consider the appropriate responses to the shareholder demand letters in view of developments in proceedings concerning the Grenfell Tower fire. In addition, the Company has settled lawsuits with another shareholder that had been pending in state court in New York and federal court in Pennsylvania concerning the shareholder’s demand to inspect certain of the Company’s books and records related to the Grenfell Tower fire and Reynobond PE. Other In addition to the matters discussed above, various other lawsuits, claims, and proceedings have been or may be instituted or asserted against Arconic, including those pertaining to environmental, product liability, safety and health, employment, and tax matters. While the amounts claimed in these other matters may be substantial, the ultimate liability cannot currently be determined because of the considerable uncertainties that exist. Therefore, it is possible that the Company’s liquidity or results of operations in a period could be materially affected by one or more of these other matters. However, based on facts currently available, management believes that the disposition of these other matters that are pending or asserted will not have a material adverse effect, individually or in the aggregate, on the results of operations, financial position or cash flows of the Company. Commitments Guarantees At June 30, 2018, Arconic had outstanding bank guarantees related to tax matters, outstanding debt, workers’ compensation, environmental obligations, energy contracts, and customs duties, among others. The total amount committed under these guarantees, which expire at various dates between 2018 and 2026, was $33 at June 30, 2018. Pursuant to the Separation and Distribution Agreement between Arconic and Alcoa Corporation, Arconic was required to provide certain guarantees for Alcoa Corporation, which had a combined fair value of $7 and $8 at June 30, 2018 and December 31, 2017, respectively, and were included in Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet. Arconic was required to provide payment guarantees for Alcoa Corporation issued on behalf of a third party, and amounts outstanding under these payment guarantees were $111 and $197 at June 30, 2018 and December 31, 2017, respectively. These guarantees expire at various times between 2018 and 2024, and relate to project financing for Alcoa Corporation’s aluminum complex in Saudi Arabia. Furthermore, Arconic was required to provide a guarantee up to an estimated present value amount of approximately $1,156 and $1,297 at June 30, 2018 and December 31, 2017, respectively, related to a long-term supply agreement for energy for an Alcoa Corporation facility in the event of an Alcoa Corporation payment default. This guarantee expires in 2047. For each guarantee, subject to its respective provisions, Arconic is secondarily liable in the event of a payment default by Alcoa Corporation. Arconic currently views the risk of an Alcoa Corporation payment default on its obligations under the respective contracts to be remote. Letters of Credit Arconic has outstanding letters of credit, primarily related to workers’ compensation, environmental obligations and leasing obligations. The total amount committed under these letters of credit, which automatically renew or expire at various dates, mostly in 2018, was $128 at June 30, 2018. Pursuant to the Separation and Distribution Agreement, Arconic was required to retain letters of credit of $53 that had previously been provided related to both Arconic and Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016. Alcoa Corporation workers’ compensation claims and letter of credit fees paid by Arconic are being proportionally billed to and are being fully reimbursed by Alcoa Corporation. Surety Bonds Arconic has outstanding surety bonds, primarily related to tax matters, contract performance, workers’ compensation, environmental-related matters, and customs duties. The total amount committed under these surety bonds, which expire at various dates, primarily in 2018, was $49 at June 30, 2018. Pursuant to the Separation and Distribution Agreement, Arconic was required to provide surety bonds related to Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016 and, as a result, Arconic has $25 in outstanding surety bonds relating to these liabilities. Alcoa Corporation workers’ compensation claims and surety bond fees paid by Arconic are being proportionately billed to and are being fully reimbursed by Alcoa Corporation.

Subsequent Events	6 Months Ended
Subsequent Events	Jun. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Management evaluated all activity of Arconic and concluded that no subsequent events have occurred that would require recognition in the Consolidated Financial Statements or disclosure in the Notes to the Consolidated Financial Statements, except as noted below: See Notes H and Q for details of subsequent events related to an uncertain tax position that was effectively settled and an ongoing tax matter in Spain. On July 31, 2018, the Company announced that it had initiated a sale process of its Building and Construction Systems (BCS) business, as part of the Company’s ongoing strategy and portfolio review that commenced in January 2018. BCS is part of the Transportation and Construction Solutions segment and generated third-party sales of approximately $1,070 for the year ended December 31, 2017.

Recently Adopted and Recently Issued Accounting Guidance (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Recently Adopted and Recently Issued Accounting Guidance	Adopted In May 2014, the FASB issued changes to the recognition of revenue from contracts with customers. These changes created a comprehensive framework for all entities in all industries to apply in the determination of when to recognize revenue and, therefore, supersede virtually all existing revenue recognition requirements and guidance. This framework is expected to result in less complex guidance in application while providing a consistent and comparable methodology for revenue recognition. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, an entity should apply the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract(s), (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract(s), and (v) recognize revenue when, or as, the entity satisfies a performance obligation. These changes became effective for Arconic on January 1, 2018. Arconic adopted this new guidance using the modified retrospective transition approach applied to those contracts that were not completed as of January 1, 2018. There was no cumulative effect adjustment to the opening balance of retained earnings in the Consolidated Balance Sheet in the first quarter of 2018, as the adoption did not result in a change to our timing of revenue recognition, which continues to be at a point in time. See Note C for further details. In January 2016, the FASB issued changes to equity investments. These changes require equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. However, an entity may choose to measure equity investments that do not have readily determinable fair values using the measurement alternative of cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer. Also, the impairment assessment of equity investments without readily determinable fair values has been simplified by requiring a qualitative assessment to identify impairment. Also, the new guidance required changes in fair value of equity securities to be recognized immediately as a component of net income instead of being reported in accumulated other comprehensive loss until the gain (loss) is realized. These changes became effective for Arconic on January 1, 2018 and have been applied on a prospective basis. Arconic elected the measurement alternative for its equity investments that do not have readily determinable fair values. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements. In August 2016, the FASB issued changes to the classification of certain cash receipts and cash payments within the statement of cash flows. The guidance identifies eight specific cash flow items and the sections where they must be presented within the statement of cash flows. These changes became effective for Arconic on January 1, 2018 and have been be applied retrospectively. As of result of the adoption, Arconic reclassified cash received related to beneficial interest in previously transferred trade accounts receivables from operating activities to investing activities in the Statement of Consolidated Cash Flows. This new accounting standard does not reflect a change in our underlying business or activities. The reclassification of cash received related to beneficial interest in previously transferred trade accounts receivables was $285 for the six months ended June 30, 2017. In addition, Arconic reclassified $52 of cash paid for debt prepayments including extinguishment costs from operating activities to financing activities for the six months ended June 30, 2017. In November 2016, the FASB issued changes to the classification of cash and cash equivalents within the statement of cash flow. Restricted cash and cash equivalents will be included within the cash and cash equivalents line on the cash flow statement and a reconciliation must be prepared to the statement of financial position. Transfers between restricted cash and cash equivalents and cash and cash equivalents will no longer be presented as cash flow activities in the Statement of Consolidated Cash Flows and for material balances of restricted cash and restricted cash equivalents Arconic will disclose information regarding the nature of the restrictions. These changes became effective for Arconic on January 1, 2018 and have been applied retrospectively. Management has determined that the adoption of this guidance did not have a material impact on the Statement of Consolidated Cash Flows. Restricted cash was $5, $4 and $5 at June 30, 2018, December 31, 2017 and June 30, 2017, respectively. In March 2017, the FASB issued changes to the presentation of net periodic pension cost and net periodic postretirement benefit cost. The new guidance requires registrants to present the service cost component of net periodic benefit cost in the same income statement line item or items as other employee compensation costs arising from services rendered during the period. Also, only the service cost component will be eligible for asset capitalization. Registrants will present the other components of net periodic benefit cost separately from the service cost component; and, the line item or items used in the income statement to present the other components of net periodic benefit cost must be disclosed. These changes became effective for Arconic on January 1, 2018 and were adopted retrospectively for the presentation of the service cost component and the other components of net periodic benefit cost in the Statement of Consolidated Operations, and prospectively for the asset capitalization of the service cost component of net periodic benefit cost. The Company recorded the service related net periodic benefit cost within Cost of goods sold, Selling, general administrative, and other expenses and Research and development expenses and recorded the non-service related net periodic benefit cost (except for the curtailment cost which was recorded in Restructuring and other charges) separately from service cost in Other expense (income), net within the Statement of Consolidated Operations. The impact of the retrospective adoption of this guidance was an increase to consolidated Operating income of $39 and $77 while there was no impact to consolidated Net income for the second quarter or six months ended June 30, 2017, respectively. In May 2017, the FASB issued clarification to guidance on the modification accounting criteria for share-based payment awards. The new guidance requires registrants to apply modification accounting unless three specific criteria are met. The three criteria are 1) the fair value of the award is the same before and after the modification, 2) the vesting conditions are the same before and after the modification and 3) the classification as a debt or equity award is the same before and after the modification. These changes became effective for Arconic on January 1, 2018 and were applied prospectively to new awards modified after adoption. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements. Issued In February 2016, the FASB issued changes to the accounting and presentation of leases. These changes require lessees to recognize a right of use asset and lease liability on the balance sheet for all leases with terms longer than 12 months. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize a right of use asset and lease liability. Also, when measuring assets and liabilities arising from a lease, optional payments should be included only if the lessee is reasonably certain to exercise an option to extend the lease, exercise a purchase option, or not exercise an option to terminate the lease. As originally released, the standards update required application at the beginning of the earliest comparative period presented at the time of adoption. However, in July 2018, the FASB provided entities the option to instead apply the provisions of the new leases guidance at the effective date, without adjusting the comparative periods presented. These changes become effective for Arconic on January 1, 2019. Arconic’s current operating lease portfolio is primarily comprised of land and buildings, plant equipment, vehicles, and computer equipment. A cross-functional implementation team is in the process of determining the scope of arrangements that will be subject to this standard as well as assessing the impact to the Company’s systems, processes and internal controls. Arconic has contracted with a third-party vendor to implement a software solution. Concurrently, Arconic is compiling lease data to be uploaded into the software solution to account for leases under the new standard. Management is evaluating the impact of these changes on the Consolidated Balance Sheet, which will require right of use assets and lease liabilities be recorded for operating leases; therefore, an estimate of the impact is not currently determinable. However, the adoption is not expected to have a material impact on the Statement of Consolidated Operations or Statement of Consolidated Cash Flows. In June 2016, the FASB added a new impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses. The CECL model applies to most debt instruments, trade receivables, lease receivables, financial guarantee contracts, and other loan commitments. The CECL model does not have a minimum threshold for recognition of impairment losses and entities will need to measure expected credit losses on assets that have a low risk of loss. These changes become effective for Arconic on January 1, 2020. Management is currently evaluating the potential impact of these changes on the Consolidated Financial Statements. In August 2017, the FASB issued guidance that will make more financial and nonfinancial hedging strategies eligible for hedge accounting. It also amends the presentation and disclosure requirements and changes how companies assess effectiveness. It is intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. These changes become effective for Arconic on January 1, 2019. For cash flow and net investment hedges existing at the date of adoption, Arconic will apply a cumulative-effect adjustment related to eliminating the separate measurement of ineffectiveness to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year in which the amendment is adopted. The amended presentation and disclosure guidance is required only prospectively. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements. In February 2018, the FASB issued guidance that allows an optional reclassification from Accumulated other comprehensive loss to Accumulated deficit for stranded tax effects resulting from the Tax Cuts and Jobs Act enacted on December 22, 2017. These changes become effective for Arconic on January 1, 2019. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements.
Revenue from Contracts with Customers	The Company's contracts with customers are comprised of acknowledged purchase orders incorporating the Company’s standard terms and conditions, or for larger customers, terms under negotiated multi-year agreements. These contracts with customers typically consist of the manufacture of products which represent single performance obligations that are satisfied upon transfer of control of the product to the customer. The Company produces fastening systems; seamless rolled rings; investment castings, including airfoils and forged jet engine components; extruded, machined and formed aircraft parts; aluminum sheet and plate; integrated aluminum structural systems; architectural extrusions; and forged aluminum commercial vehicle wheels. Transfer of control is assessed based on alternative use of the products we produce and our enforceable right to payment for performance to date under the contract terms. Transfer of control and revenue recognition generally occur upon shipment or delivery of the product, which is when title, ownership and risk of loss pass to the customer and is based on the applicable shipping terms. The shipping terms vary across all businesses and depend on the product, the country of origin, and the type of transportation (truck, train, or vessel). An invoice for payment is issued at time of shipment. The Company’s objective is to have net 30-day terms. Our business units set commercial terms on which Arconic sells products to its customers. These terms are influenced by industry custom, market conditions, product line (specialty versus commodity products), and other considerations.
Segment Information	Arconic is a global leader in lightweight metals engineering and manufacturing. Arconic’s innovative, multi-material products, which include aluminum, titanium, and nickel, are used worldwide in aerospace, automotive, commercial transportation, building and construction, industrial applications, defense, and packaging. Arconic’s segments are organized by product on a worldwide basis. In the first quarter of 2018, the Company changed its primary measure of segment performance from Adjusted earnings before interest, tax, depreciation and amortization (“Adjusted EBITDA”) to Segment operating profit, which more closely aligns segment performance with Operating income as presented in the Statement of Consolidated Operations. Segment performance under Arconic’s management reporting system is evaluated based on a number of factors; however, the primary measure of performance is Segment operating profit. Arconic’s definition of Segment operating profit is Operating income excluding Special items. Special items include Restructuring and other charges and Impairment of goodwill. Segment operating profit also includes certain items that, under the previous segment performance measure, were recorded in Corporate, such as the impact of LIFO inventory accounting, metal price lag, intersegment profit eliminations, and derivative activities. Segment operating profit may not be comparable to similarly titled measures of other companies. Prior period financial information has been recast to conform to current year presentation. Differences between segment totals and consolidated Arconic are in Corporate.
Earnings Per Share	Basic earnings per share (EPS) amounts are computed by dividing earnings, after the deduction of preferred stock dividends declared, by the average number of common shares outstanding. Diluted EPS amounts assume the issuance of common stock for all potentially dilutive share equivalents outstanding.
Receivables	Cash receipts from customer payments on sold receivables (which are cash receipts on the underlying trade receivables that have been previously sold in this program) as well as cash receipts and cash disbursements from draws and repayments under the program are presented as cash receipts from sold receivables within investing activities in the Statement of Consolidated Cash Flows.
Fair Value	The fair value of Long-term debt, less amount due within one year was based on quoted market prices for public debt and on interest rates that are currently available to Arconic for issuance of debt with similar terms and maturities for non-public debt. The fair value amounts for all Long-term debt were classified in Level 2 of the fair value hierarchy.

- Definition

Disclosure of accounting policy for trade and other accounts receivable, and finance, loan and lease receivables, including those classified as held for investment and held for sale. This disclosure may include (1) the basis at which such receivables are carried in the entity's statements of financial position (2) how the level of the valuation allowance for receivables is determined (3) when impairments, charge-offs or recoveries are recognized for such receivables (4) the treatment of origination fees and costs, including the amortization method for net deferred fees or costs (5) the treatment of any premiums or discounts or unearned income (6) the entity's income recognition policies for such receivables, including those that are impaired, past due or placed on nonaccrual status and (7) the treatment of foreclosures or repossessions (8) the nature and amount of any guarantees to repurchase receivables.

+ References + Details

Revenue from Contracts with Customers (Tables)

6 Months Ended

Jun. 30, 2018

Revenue from Contract with Customer [Abstract]

Revenue from External Customers by Products and Services



	Engineered Products and Solutions		Global Rolled Products		Transportation and Construction Solutions		Total Segment
Second quarter ended June 30, 2018
Aerospace	$	1,241	$	226	$	—	$	1,467
Transportation	119		612		253		984
Building and construction	—		60		297		357
Industrial and other	236		553		12		801
Total end-market revenue	$	1,596	$	1,451	$	562	$	3,609

Second quarter ended June 30, 2017
Aerospace	$	1,141	$	241	$	—	$	1,382
Transportation	97		475		200		772
Building and construction	—		51		283		334
Industrial and other	247		504		21		772
Total end-market revenue	$	1,485	$	1,271	$	504	$	3,260

Six months ended June 30, 2018
Aerospace	$	2,431	$	425	$	—	$	2,856
Transportation	216		1,210		496		1,922
Building and construction	—		108		582		690
Industrial and other	490		1,074		21		1,585
Total end-market revenue	$	3,137	$	2,817	$	1,099	$	7,053

Six months ended June 30, 2017
Aerospace	$	2,296	$	456	$	—	$	2,752
Transportation	190		968		373		1,531
Building and construction	—		100		545		645
Industrial and other	486		995		42		1,523
Total end-market revenue	$	2,972	$	2,519	$	960	$	6,451

Segment Information (Tables)

6 Months Ended

Jun. 30, 2018

Segment Reporting [Abstract]

Schedule of Operating Results of Arconic's Reportable Segments

The operating results of Arconic’s reportable segments were as follows:



	Engineered Products and Solutions		Global Rolled Products		Transportation and Construction Solutions		Total Segment
Second quarter ended June 30, 2018
Sales:
Third-party sales	$	1,596	$	1,451	$	562	$	3,609
Intersegment sales	—		46		—		46
Total sales	$	1,596	$	1,497	$	562	$	3,655
Profit and loss:
Segment operating profit	$	212	$	123	$	97	$	432
Restructuring and other charges	9		1		—		10
Provision for depreciation and amortization	70		53		12		135

Second quarter ended June 30, 2017
Sales:
Third-party sales	$	1,485	$	1,271	$	504	$	3,260
Intersegment sales	—		37		—		37
Total sales	$	1,485	$	1,308	$	504	$	3,297
Profit and loss:
Segment operating profit	$	250	$	133	$	71	$	454
Restructuring and other charges	8		17		6		31
Provision for depreciation and amortization	66		51		12		129



	Engineered Products and Solutions		Global Rolled Products		Transportation and Construction Solutions		Total Segment
Six months ended June 30, 2018
Sales:
Third-party sales	$	3,137	$	2,817	$	1,099	$	7,053
Intersegment sales	—		88		—		88
Total sales	$	3,137	$	2,905	$	1,099	$	7,141
Profit and loss:
Segment operating profit	$	433	$	235	$	164	$	832
Restructuring and other charges	10		—		—		10
Provision for depreciation and amortization	141		104		25		270

Six months ended June 30, 2017
Sales:
Third-party sales	$	2,972	$	2,519	$	960	$	6,451
Intersegment sales	—		71		—		71
Total sales	$	2,972	$	2,590	$	960	$	6,522
Profit and loss:
Segment operating profit	$	497	$	269	$	139	$	905
Restructuring and other charges	14		74		9		97
Provision for depreciation and amortization	130		101		24		255

Schedule Of Segment Reporting Information To Consolidate Net Income Loss Attributable To Parent

The following table reconciles Total segment operating profit to Consolidated income before income taxes:



	Second quarter ended						Six months ended
	June 30,						June 30,
	2018			2017			2018			2017
Total segment operating profit	$	432		$	454		$	832		$	905
Unallocated amounts:
Restructuring and other charges	(15		)	(26		)	(22		)	(99		)
Corporate expense	(93		)	(108		)	(153		)	(203		)
Consolidated operating income	$	324		$	320		$	657		$	603
Interest expense	(89		)	(183		)	(203		)	(298		)
Other (expense) income, net	(41		)	132			(61		)	448
Consolidated income before income taxes	$	194		$	269		$	393		$	753

Reconciliation of Assets from Segment to Consolidated

The following table reconciles Total segment assets to Consolidated assets:



	June 30, 2018		December 31, 2017
Total segment assets	$	15,687	$	15,321
Unallocated amounts:
Cash and cash equivalents	1,455		2,150
Deferred income taxes	626		743
Corporate fixed assets, net	304		310
Fair value of derivative contracts	57		91
Other	90		103
Consolidated assets	$	18,219	$	18,718

The total assets of Arconic's reportable segment were as follows:



	June 30, 2018		December 31, 2017
Engineered Products and Solutions	$	10,447	$	10,325
Global Rolled Products	4,153		3,955
Transportation and Construction Solutions	1,087		1,041
Total segment assets	$	15,687	$	15,321

Restructuring and Other Charges (Tables)

6 Months Ended

Jun. 30, 2018

Restructuring and Related Activities [Abstract]

Activity and Reserve Balances for Restructuring Charges

Activity and reserve balances for restructuring and other charges were as follows:



	Layoff costs			Other exit costs			Total
Reserve balances at December 31, 2016	$	50		$	9		$	59
Cash payments	(59		)	(6		)	(65		)
Restructuring charges	64			1			65
Other⁽¹⁾	1			(2		)	(1		)
Reserve balances at December 31, 2017	56			2			58
Cash payments	(30		)	—			(30		)
Restructuring charges	23			5			28
Other⁽¹⁾	(23		)	—			(23		)
Reserve balances at June 30, 2018	$	26		$	7		$	33


⁽¹⁾	Other includes reversals of previously recorded restructuring charges and the effects of foreign currency translation. In 2018, Other for layoff costs also included a reclassification of $14 in pension costs, as this liability was reflected in Arconic’s separate liability for pension obligations. In 2017, Other for layoff costs also included a reclassification of a stock awards reversal of $13.

Other Expense (Income), Net (Tables)

6 Months Ended

Jun. 30, 2018

Other Income and Expenses [Abstract]

Schedule of Other Nonoperating Income (Expense)



	Second quarter ended						Six months ended
	June 30,						June 30,
	2018			2017			2018			2017
Non-service related net periodic benefit cost	$	28		$	39		$	56		$	77
Interest income	(4		)	(4		)	(10		)	(8		)
Foreign currency gains (losses), net	17			2			14			(3		)
Net loss (gain) from asset sales	2			(166		)	5			(515		)
Other, net	(2		)	(3		)	(4		)	1
	$	41		$	(132	)	$	61		$	(448	)

Pension and Other Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2018

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost

The components of net periodic benefit cost were as follows:



	Second quarter ended						Six months ended
	June 30,						June 30,
	2018			2017			2018			2017
Pension benefits
Service cost	$	8		$	21		$	28		$	44
Interest cost	55			58			110			116
Expected return on plan assets	(77		)	(82		)	(154		)	(165		)
Recognized net actuarial loss	42			55			84			110
Amortization of prior service cost (benefit)	1			2			2			3
Curtailments	9			—			14			—
Net periodic benefit cost⁽¹⁾	$	38		$	54		$	84		$	108

Other postretirement benefits
Service cost	$	2		$	2		$	4		$	4
Interest cost	7			7			14			15
Recognized net actuarial loss	2			1			4			2
Amortization of prior service cost (benefit)	(2		)	(2		)	(4		)	(4		)
Net periodic benefit cost⁽¹⁾	$	9		$	8		$	18		$	17


⁽¹⁾	Service cost was included within Cost of goods sold, Selling, general administrative, and other expenses, and Research and development expenses; curtailments were included in Restructuring and other charges; and all other cost components were recorded in Other expense (income), net in the Statement of Consolidated Operations.

Income Taxes (Tables)

6 Months Ended

Jun. 30, 2018

Income Tax Disclosure [Abstract]

Schedule of Income Tax Provisions

The tax provisions for the second quarter and six months ended June 30, 2018 and 2017 were comprised of the following:



	Second quarter ended					Six months ended
	June 30,					June 30,
	2018		2017			2018		2017
Pre-tax income at estimated annual effective income tax rate before discrete items	$	52	$	60		$	106	$	214
Catch-up adjustment to revalue previous quarter pre-tax income at current estimated annual effective tax rate	1		—			—		—
Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized	—		(3		)	1		4
Other discrete items	21		—			23		1
Provision for income taxes	$	74	$	57		$	130	$	219

Earnings Per Share (Tables)

6 Months Ended

Jun. 30, 2018

Earnings Per Share [Abstract]

Reconciliation of Information Used to Compute Basic and Diluted EPS

The information used to compute basic and diluted EPS attributable to Arconic common shareholders was as follows (shares in millions):



	Second quarter ended						Six months ended
	June 30,						June 30,
	2018		2017				2018			2017
Net income	$	120	$	212			$	263		$	534
Less: Preferred stock dividends declared	—		(18		)		(1		)	(35		)
Net income available to Arconic common shareholders - basic	120		194				262			499
Add: Interest expense related to convertible notes	3		2				6			4
Add: Dividends related to mandatory convertible preferred stock	—		—				—			34
Net income available to Arconic common shareholders - diluted	$	123	$	196		—	$	268		$	537

Average shares outstanding - basic	483		441				483			440
Effect of dilutive securities:
Stock options	—		2				—			2
Stock and performance awards	5		5				5			5
Mandatory convertible preferred stock	—		—				—			39
Convertible notes	14		14				14			14
Average shares outstanding - diluted	502		462				502			500

Schedule of Anti Dilutive Securities Excluded From Computation of Weighted Average Shares Outstanding

The following shares were excluded from the calculation of average shares outstanding – diluted as their effect was anti-dilutive (shares in millions).



	Second quarter ended		Six months ended
	June 30,		June 30,
	2018	2017	2018	2017
Mandatory convertible preferred stock	—	39	—	—
Stock options⁽¹⁾	9	7	9	7


⁽¹⁾	The average exercise price of options per share was $26.80 for the second quarter and six months ended June 30, 2018 and $28.85 for the second quarter and six months ended June 30, 2017.

Accumulated Other Comprehensive Loss (Tables)

6 Months Ended

Jun. 30, 2018

Equity [Abstract]

Summary of Changes in Accumulated Other Comprehensive (Loss) by Component

The following table details the activity of the four components that comprise Accumulated other comprehensive loss for both Arconic’s shareholders and noncontrolling interests:



	Arconic						Noncontrolling Interests
Second quarter ended June 30,	2018			2017			2018		2017
Pension and other postretirement benefits (G)
Balance at beginning of period	$	(2,087	)	$	(1,979	)	$	—	$	—
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	(15		)	17			—		—
Tax benefit (expense)	3			(5		)	—		—
Total Other comprehensive (loss) income before reclassifications, net of tax	(12		)	12			—		—
Amortization of net actuarial loss and prior service cost⁽¹⁾	52			56			—		—
Tax expense⁽²⁾	(11		)	(20		)	—		—
Total amount reclassified from Accumulated other comprehensive loss, net of tax⁽⁵⁾	41			36			—		—
Total Other comprehensive income	29			48			—		—
Balance at end of period	$	(2,058	)	$	(1,931	)	$	—	$	—
Foreign currency translation
Balance at beginning of period	$	(315	)	$	(622	)	$	—	$	(2	)
Other comprehensive (loss) income⁽³⁾	(201		)	99			—		—
Balance at end of period	$	(516	)	$	(523	)	$	—	$	(2	)
Available-for-sale securities
Balance at beginning of period	$	(2	)	$	99		$	—	$	—
Other comprehensive loss⁽⁴⁾	(2		)	(101		)	—		—
Balance at end of period	$	(4	)	$	(2	)	$	—	$	—
Cash flow hedges
Balance at beginning of period	$	18		$	4		$	—	$	—
Other comprehensive income (loss):
Net change from periodic revaluations	9			(4		)	—		—
Tax (expense) benefit	(1		)	1			—		—
Total Other comprehensive income (loss) before reclassifications, net of tax	8			(3		)	—		—
Net amount reclassified to earnings	(4		)	1			—		—
Tax benefit⁽²⁾	—			—			—		—
Total amount reclassified from Accumulated other comprehensive loss, net of tax⁽⁵⁾	(4		)	1			—		—
Total Other comprehensive income (loss)	4			(2		)	—		—
Balance at end of period	$	22		$	2		$	—	$	—

Total balance at end of period	$	(2,556	)	$	(2,454	)	$	—	$	(2	)


⁽¹⁾	These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note G).


⁽²⁾	These amounts were included in Provision for income taxes on the accompanying Statement of Consolidated Operations.


⁽³⁾	In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings.


⁽⁴⁾	Realized gains and losses were included in Other expense (income), net on the accompanying Statement of Consolidated Operations.


⁽⁵⁾	A positive amount indicates a corresponding charge to earnings and a negative amount indicates a corresponding benefit to earnings.



	Arconic						Noncontrolling Interests
Six months ended June 30,	2018			2017			2018		2017
Pension and other postretirement benefits (G)
Balance at beginning of period	$	(2,230	)	$	(2,010	)	$	—	$	—
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	122			11			—		—
Tax expense	(28		)	(4		)	—		—
Total Other comprehensive income before reclassifications, net of tax	94			7			—		—
Amortization of net actuarial loss and prior service cost⁽¹⁾	100			111			—		—
Tax expense⁽²⁾	(22		)	(39		)	—		—
Total amount reclassified from Accumulated other comprehensive loss, net of tax⁽⁵⁾	78			72			—		—
Total Other comprehensive income	172			79			—		—
Balance at end of period	$	(2,058	)	$	(1,931	)	$	—	$	—
Foreign currency translation
Balance at beginning of period	$	(437	)	$	(689	)	$	—	$	(2	)
Other comprehensive (loss) income⁽³⁾	(79		)	166			—		—
Balance at end of period	$	(516	)	$	(523	)	$	—	$	(2	)
Available-for-sale securities
Balance at beginning of period	$	(2	)	$	132		$	—	$	—
Other comprehensive loss⁽⁴⁾	(2		)	(134		)	—		—
Balance at end of period	$	(4	)	$	(2	)	$	—	$	—
Cash flow hedges
Balance at beginning of period	$	25		$	(1	)	$	—	$	—
Other comprehensive (loss) income:
Net change from periodic revaluations	3			4			—		—
Tax expense	—			(2		)	—		—
Total Other comprehensive income before reclassifications, net of tax	3			2			—		—
Net amount reclassified to earnings	(7		)	1			—		—
Tax benefit⁽²⁾	1			—			—		—
Total amount reclassified from Accumulated other comprehensive loss, net of tax⁽⁵⁾	(6		)	1			—		—
Total Other comprehensive (loss) income	(3		)	3			—		—
Balance at end of period	$	22		$	2		$	—	$	—

Total balance at end of period	$	(2,556	)	$	(2,454	)	$	—	$	(2	)


⁽¹⁾	These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note G).


⁽²⁾	These amounts were included in Provision for income taxes on the accompanying Statement of Consolidated Operations.


⁽³⁾	In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings.


⁽⁴⁾	Realized gains and losses were included in Other expense (income), net on the accompanying Statement of Consolidated Operations.


⁽⁵⁾	A positive amount indicates a corresponding charge to earnings and a negative amount indicates a corresponding benefit to earnings.

Inventories (Tables)

6 Months Ended

Jun. 30, 2018

Inventory Disclosure [Abstract]

Schedule of Inventory Components



	June 30, 2018		December 31, 2017
Finished goods	$	682	$	669
Work-in-process	1,485		1,349
Purchased raw materials	401		381
Operating supplies	91		81
Total inventories	$	2,659	$	2,480

Property, Plants, and Equipment, Net (Tables)

6 Months Ended

Jun. 30, 2018

Property, Plant and Equipment [Abstract]

Property, Plants, and Equipment, Net



	June 30, 2018		December 31, 2017
Land and land rights	$	139	$	140
Structures	2,376		2,395
Machinery and equipment	9,148		8,830
	11,663		11,365
Less: accumulated depreciation and amortization	6,674		6,392
	4,989		4,973
Construction work-in-progress	593		621
	$	5,582	$	5,594

Debt (Tables)

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Schedule of Long-Term Debt



	June 30, 2018			December 31, 2017
5.72% Notes, due 2019	$	—		$	500
1.63% Convertible Notes, due 2019	403			403
6.150% Notes, due 2020	1,000			1,000
5.40% Notes due 2021	1,250			1,250
5.87% Notes, due 2022	627			627
5.125% Notes, due 2024	1,250			1,250
5.90% Notes, due 2027	625			625
6.75% Bonds, due 2028	300			300
5.95% Notes, due 2037	625			625
Iowa Finance Authority Loan, due 2042	250			250
Other⁽¹⁾	(15		)	(23		)
Total debt	6,315			6,807
Less: amount due within one year	3			1
Total long-term debt	$	6,312		$	6,806


⁽¹⁾	Includes various financing arrangements related to subsidiaries, unamortized debt discounts related to outstanding notes and bonds listed in the table above, an equity option related to the convertible notes due in 2019, and unamortized debt issuance costs.

Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Carrying Values and Fair Values of Financial Instruments

The following table summarizes Arconic’s financial liabilities that were not carried at fair value at June 30, 2018 and December 31, 2017:



	June 30, 2018				December 31, 2017
	Carrying value		Fair value		Carrying value		Fair value
Long-term debt, less amount due within one year	$	6,312	$	6,457	$	6,806	$	7,443

Basis of Presentation (Details)	3 Months Ended	6 Months Ended	12 Months Ended
Basis of Presentation (Details)	Mar. 31, 2018 USD ($)	Jun. 30, 2018 USD ($) reporting_unit	Dec. 31, 2017 USD ($) reporting_unit
Basis Of Presentation [Line Items]
Number of reporting units \| reporting_unit		3	4
Goodwill, impairment loss		$ 0
Goodwill		$ 4,518,000,000	$ 4,535,000,000
Arconic Engines
Basis Of Presentation [Line Items]
Goodwill	$ 2,095,000,000
Alcoa Fastening Systems And Rings
Basis Of Presentation [Line Items]
Goodwill	1,623,000,000
Arconic Engineered Structures
Basis Of Presentation [Line Items]
Goodwill	$ 517,000,000
Minimum
Basis Of Presentation [Line Items]
Percentage of goodwill allocated to reporting units	92.00%

Recently Adopted and Recently Issued Accounting Guidance (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Mar. 30, 2012	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Accounting Policies [Abstract]
Restricted cash		$ 5	$ 5	$ 5	$ 5	$ 4
Summary Of Significant Accounting Policies [Line Items]
Reclassification of cash received related to beneficial interest in previously transferred trade accounts receivables	$ 50			420	285
Reclassification of cash paid for debt prepayments including extinguishment costs from operating to financing activities				17	52
Adjustment to operating income based on adoption of new accounting guidance		$ 324	320	$ 657	603
ASU 2016-15
Summary Of Significant Accounting Policies [Line Items]
Reclassification of cash paid for debt prepayments including extinguishment costs from operating to financing activities					(52)
Adjustments for New Accounting Pronouncement
Summary Of Significant Accounting Policies [Line Items]
Adjustment to operating income based on adoption of new accounting guidance			$ 39		$ 77

Revenue from Contracts with Customers - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue, shipping payment terms		30 days
Customer claims for new product introductions	$ 38	$ 38

Revenue from Contracts with Customers - Segment Revenue By Product (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	$ 3,609	$ 3,260	$ 7,053	$ 6,451
Aerospace
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	1,467	1,382	2,856	2,752
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	984	772	1,922	1,531
Building and construction
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	357	334	690	645
Industrial and other
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	801	772	1,585	1,523
Engineered Products and Solutions
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	1,596	1,485	3,137	2,972
Engineered Products and Solutions \| Aerospace
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	1,241	1,141	2,431	2,296
Engineered Products and Solutions \| Transportation
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	119	97	216	190
Engineered Products and Solutions \| Building and construction
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	0	0	0	0
Engineered Products and Solutions \| Industrial and other
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	236	247	490	486
Global Rolled Products
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	1,451	1,271	2,817	2,519
Global Rolled Products \| Aerospace
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	226	241	425	456
Global Rolled Products \| Transportation
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	612	475	1,210	968
Global Rolled Products \| Building and construction
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	60	51	108	100
Global Rolled Products \| Industrial and other
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	553	504	1,074	995
Transportation and Construction Solutions
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	562	504	1,099	960
Transportation and Construction Solutions \| Aerospace
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	0	0	0	0
Transportation and Construction Solutions \| Transportation
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	253	200	496	373
Transportation and Construction Solutions \| Building and construction
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	297	283	582	545
Transportation and Construction Solutions \| Industrial and other
Disaggregation of Revenue [Line Items]
Revenue from contract with customers	$ 12	$ 21	$ 21	$ 42

Segment Information - Schedule of Operating Results of Arconic's Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total sales	$ 3,573	$ 3,261	$ 7,018	$ 6,453
Segment operating profit	432	454	832	905
Restructuring and other charges	10	31	10	97
Provision for depreciation and amortization	135	129	270	255
Operating Segments
Segment Reporting Information [Line Items]
Total sales	3,655	3,297	7,141	6,522
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total sales	46	37	88	71
Third-Party Sales \| Operating Segments
Segment Reporting Information [Line Items]
Total sales	3,609	3,260	7,053	6,451
Engineered Products and Solutions
Segment Reporting Information [Line Items]
Segment operating profit	212	250	433	497
Restructuring and other charges	9	8	10	14
Provision for depreciation and amortization	70	66	141	130
Engineered Products and Solutions \| Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,596	1,485	3,137	2,972
Engineered Products and Solutions \| Intersegment Eliminations
Segment Reporting Information [Line Items]
Total sales	0	0	0	0
Engineered Products and Solutions \| Third-Party Sales \| Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,596	1,485	3,137	2,972
Global Rolled Products
Segment Reporting Information [Line Items]
Segment operating profit	123	133	235	269
Restructuring and other charges	1	17	0	74
Provision for depreciation and amortization	53	51	104	101
Global Rolled Products \| Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,497	1,308	2,905	2,590
Global Rolled Products \| Intersegment Eliminations
Segment Reporting Information [Line Items]
Total sales	46	37	88	71
Global Rolled Products \| Third-Party Sales \| Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,451	1,271	2,817	2,519
Transportation and Construction Solutions
Segment Reporting Information [Line Items]
Segment operating profit	97	71	164	139
Restructuring and other charges	0	6	0	9
Provision for depreciation and amortization	12	12	25	24
Transportation and Construction Solutions \| Operating Segments
Segment Reporting Information [Line Items]
Total sales	562	504	1,099	960
Transportation and Construction Solutions \| Intersegment Eliminations
Segment Reporting Information [Line Items]
Total sales	0	0	0	0
Transportation and Construction Solutions \| Third-Party Sales \| Operating Segments
Segment Reporting Information [Line Items]
Total sales	$ 562	$ 504	$ 1,099	$ 960

Segment Information - Schedule of Combined Segment Adjusted EBITDA to Net Income Attributable to Arconic (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total segment operating profit	$ 432	$ 454	$ 832	$ 905
Restructuring and other charges	(15)	(26)	(22)	(99)
Operating income	324	320	657	603
Interest expense	(89)	(183)	(203)	(298)
Other (expense) income, net	(41)	132	(61)	448
Income before income taxes	194	269	393	753
Segment Reconciling Items
Segment Reporting Information [Line Items]
Restructuring and other charges	(15)	(26)	(22)	(99)
Corporate expense	(93)	(108)	(153)	(203)
Operating income	324	320	657	603
Interest expense	(89)	(183)	(203)	(298)
Other (expense) income, net	(41)	132	(61)	448
Income before income taxes	$ 194	$ 269	$ 393	$ 753

Segment Information - Assets By Reportable Segment (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total segment assets	$ 18,219	$ 18,718
Operating Segments
Segment Reporting Information [Line Items]
Total segment assets	15,687	15,321
Engineered Products and Solutions
Segment Reporting Information [Line Items]
Total segment assets	10,447	10,325
Global Rolled Products
Segment Reporting Information [Line Items]
Total segment assets	4,153	3,955
Transportation and Construction Solutions
Segment Reporting Information [Line Items]
Total segment assets	$ 1,087	$ 1,041

Segment Information - Schedule of Segment Reporting Information to Consolidated Assets (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total segment assets	$ 18,219	$ 18,718
Cash and cash equivalents	1,455	2,150
Corporate fixed assets, net	5,582	5,594
Operating Segments
Segment Reporting Information [Line Items]
Total segment assets	15,687	15,321
Segment Reconciling Items
Segment Reporting Information [Line Items]
Cash and cash equivalents	1,455	2,150
Deferred income taxes	626	743
Corporate fixed assets, net	304	310
Fair value of derivative contracts	57	91
Other	$ 90	$ 103

Restructuring and Other Charges - Additional Information (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) employee position	Jun. 30, 2017 USD ($) position	Jun. 30, 2018 USD ($) employee position	Jun. 30, 2017 USD ($) position	Dec. 31, 2017 USD ($) employee
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 15	$ 26	$ 22	$ 99
Restructuring and other charges after tax and noncontrolling interest	12	$ 17	$ 17	$ 86
Number of employees associated with layoff costs \| position		352	40	680
Reversal of forfeited executive stock compensation		$ 13		$ 13
Severance costs		$ 7		7
Cash payments made against the layoff reserves			$ 30		$ 65
New York office
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	5		5
Restructuring and other charges after tax	$ 4		$ 4
Fusina, Italy
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				60
Restructuring and other charges after tax				$ 60
Corporate
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs \| position		20	16	62
Engineered Products and Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs \| position	24	129	24	243
Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs \| position		110		242
Transportation and Construction Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs \| position		93		133
Pension Curtailment Charge
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 9		$ 14
Restructuring and other charges after tax	7		11
Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	4	$ 29	8	$ 48
Restructuring and other charges after tax	3	19	6	32
Other Miscellaneous Items
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	2	4	4	1
Restructuring and other charges after tax	2	3	3	0
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	5	1	9	2
Restructuring and other charges after tax and noncontrolling interest	$ 4	1	$ 7	2
Reversal of Forfeited Executive Stock Compensation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		6		6
Restructuring and other charges after tax		$ 4		$ 4
Restructuring Programs Layoffs 2018
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs \| employee			40
Approximate number of employees already laid off \| employee	20		20
Cash payments made against the layoff reserves	$ 2		$ 3
Restructuring Programs Layoffs 2017
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs \| employee			760		830
Approximate number of employees already laid off \| employee	530		530
Cash payments made against the layoff reserves	$ 8		$ 23
Restructuring Programs Layoffs 2016
Restructuring Cost and Reserve [Line Items]
Cash payments made against the layoff reserves	$ 0		$ 4

Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			$ 58	$ 59	$ 59
Cash payments			(30)		(65)
Restructuring charges			28		65
Other			(23)		(1)
Restructuring reserve ending balance	$ 33		33		58
Restructuring and other charges	15	$ 26	22	99
Layoff costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			56	50	50
Cash payments			(30)		(59)
Restructuring charges			23		64
Other			(23)		1
Restructuring reserve ending balance	26		26		56
Other exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			2	$ 9	9
Cash payments			0		(6)
Restructuring charges			5		1
Other			0		(2)
Restructuring reserve ending balance	$ 7		7		2
Pension costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges			$ 14
Stock awards reversal
Restructuring Reserve [Roll Forward]
Restructuring and other charges					$ 13

Other Expense (Income), Net - Schedule (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Income and Expenses [Abstract]
Non-service related net periodic benefit cost	$ 28	$ 39	$ 56	$ 77
Interest income	(4)	(4)	(10)	(8)
Foreign currency gains (losses), net	17	2	14	(3)
Net loss (gain) from asset sales	2	(166)	5	(515)
Other, net	(2)	(3)	(4)	1
Total	$ 41	$ (132)	$ 61	$ (448)

Other Expense (Income), Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain from assets sales	$ (2)	$ 166	$ (5)	$ 515
Alcoa Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain from assets sales		$ 167		351
Cash received on sale of operations				$ 888

Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Curtailments	$ 9
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	$ 21	$ 28	$ 44
Interest cost	55	58	110	116
Expected return on plan assets	(77)	(82)	(154)	(165)
Recognized net actuarial loss	42	55	84	110
Amortization of prior service cost (benefit)	1	2	2	3
Curtailments	9	0	14	0
Net periodic benefit cost	38	54	84	108
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2	4	4
Interest cost	7	7	14	15
Recognized net actuarial loss	2	1	4	2
Amortization of prior service cost (benefit)	(2)	(2)	(4)	(4)
Net periodic benefit cost	$ 9	$ 8	$ 18	$ 17

Pension and Other Postretirement Benefits - Additional Information (Details)				1 Months Ended		3 Months Ended		6 Months Ended
	Apr. 13, 2018 employee	Apr. 01, 2018 USD ($)	Nov. 01, 2016 USD ($) Installments	Mar. 31, 2018 USD ($)	Apr. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits						$ 29,000,000	$ 48,000,000	$ 172,000,000	$ 79,000,000
Curtailments						9,000,000
Cash contribution term to pension plan			30 months
Number of installments \| Installments			3
Minimum required cash contribution to pension plan			$ 50,000,000
Aggregate cash cash contribution to pension plan			$ 150,000,000
Cash payments made for pension and other post-retirement benefits				$ 50,000,000	$ 50,000,000
Labor agreement, duration	5 years
Labor agreement, number of employees \| employee	1,300
Defined benefit plan, labor agreement, employees subject to retirement benefit increase \| employee	300
Pension benefits
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Curtailments						$ 9,000,000	$ 0	$ 14,000,000	$ 0
UNITED STATES \| Pension benefits
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Decrease in obligation, pension benefits		$ 136,000,000
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits		141,000,000
Curtailments		$ 5,000,000

Income Taxes - Additional Information (Details) € in Millions, $ in Millions	3 Months Ended				6 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 EUR (€)	Jun. 30, 2018 USD ($)	Jun. 30, 2017	Jun. 30, 2018 USD ($)	Jun. 30, 2017	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, percent					27.00%	28.40%
Effective income tax rate reconciliation, including discrete items, percent			38.10%	21.20%
Discrete income tax expense			$ 21
Tax Cuts And Jobs Act of 2017, incomplete accounting, provisional income tax expense (benefit)					$ 21		$ 272
Tax Cuts and Jobs Act of 2017, incomplete accounting, transition tax			$ 18		18
Charges recorded for AMT credits					$ 3
Alcoa Corporation
Subsequent Event [Line Items]
Tax agreement, indemnification of ultimate liability, percent			49.00%		49.00%
Forecast
Subsequent Event [Line Items]
FIN 48 reserve	$ 38
Forecast \| Alcoa Corporation
Subsequent Event [Line Items]
Tax agreement, indemnification of ultimate liability, percent	49.00%	49.00%
Forecast \| Spain
Subsequent Event [Line Items]
Potential impact to provision for income taxes	$ 59	€ 51

Income Taxes - Summary of Tax Provisions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Pretax income at estimated annual effective income tax rate before discrete items	$ 52	$ 60	$ 106	$ 214
Catch-up adjustment to revalue previous quarter pre-tax income at current estimated annual effective tax rate	1	0	0	0
Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized	0	(3)	1	4
Other discrete items	21	0	23	1
Provision for income taxes	$ 74	$ 57	$ 130	$ 219

Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 120	$ 212	$ 263	$ 534
Less: Preferred stock dividends declared	0	(18)	(1)	(35)
Net income available to Arconic common shareholders - basic	120	194	262	499
Add: Interest expense related to convertible notes	3	2	6	4
Add: Dividends related to mandatory convertible preferred stock	0	0	0	34
Net income available to Arconic common shareholders - diluted	$ 123	$ 196	$ 268	$ 537
Average shares outstanding - basic (in shares)	483	441	483	440
Effect of dilutive securities:
Stock options (in shares)	0	2	0	2
Stock and performance awards (in shares)	5	5	5	5
Mandatory convertible preferred stock (in shares)	0	0	0	39
Convertible notes (in shares)	14	14	14	14
Weighted average shares outstanding - diluted (in shares)	502	462	502	500

Earnings Per Share - Schedule of Anti Dilutive Securities Excluded From Computation of Weighted Average Shares Outstanding (Details) - $ / shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Mandatory convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	0	39	0	0
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	9	7	9	7
Weighted average exercise price of options (in usd per share)	$ 26.80	$ 28.85	$ 26.80	$ 28.85

Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period			$ 4,924	$ 5,141
Total Other comprehensive (loss) income, net of tax	$ (170)	$ 44	88	114
Balance at end of period	5,218	5,753	5,218	5,753
Arconic
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period			(2,644)	(2,568)
Total Other comprehensive (loss) income, net of tax			88	114
Balance at end of period	(2,556)	(2,454)	(2,556)	(2,454)
Pension and other postretirement benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,087)	(1,979)	(2,230)	(2,010)
Other comprehensive income (loss), before reclassifications, before tax	(15)	17	122	11
Tax benefit (expense)	3	(5)	(28)	(4)
Total Other comprehensive (loss) income before reclassifications, net of tax	(12)	12	94	7
Reclassification from accumulated other comprehensive income, before tax	52	56	100	111
Tax (expense) benefit	(11)	(20)	(22)	(39)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	41	36	78	72
Total Other comprehensive (loss) income, net of tax	29	48	172	79
Balance at end of period	(2,058)	(1,931)	(2,058)	(1,931)
Foreign currency translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(315)	(622)	(437)	(689)
Total Other comprehensive (loss) income, net of tax	(201)	99	(79)	166
Balance at end of period	(516)	(523)	(516)	(523)
Available-for-sale securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2)	99	(2)	132
Total Other comprehensive (loss) income, net of tax	(2)	(101)	(2)	(134)
Balance at end of period	(4)	(2)	(4)	(2)
Cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	18	4	25	(1)
Other comprehensive income (loss), before reclassifications, before tax	9	(4)	3	4
Tax benefit (expense)	(1)	1	0	(2)
Total Other comprehensive (loss) income before reclassifications, net of tax	8	(3)	3	2
Reclassification from accumulated other comprehensive income, before tax	(4)	1	(7)	1
Tax (expense) benefit	0	0	1	0
Total amount reclassified from Accumulated other comprehensive loss, net of tax	(4)	1	(6)	1
Total Other comprehensive (loss) income, net of tax	4	(2)	(3)	3
Balance at end of period	22	2	22	2
Noncontrolling Interests
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at end of period	0	(2)	0	(2)
Pension and other postretirement benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	0	0	0	0
Other comprehensive income (loss), before reclassifications, before tax	0	0	0	0
Tax benefit (expense)	0	0	0	0
Total Other comprehensive (loss) income before reclassifications, net of tax	0	0	0	0
Reclassification from accumulated other comprehensive income, before tax	0	0	0	0
Tax (expense) benefit	0	0	0	0
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0	0	0	0
Total Other comprehensive (loss) income, net of tax	0	0	0	0
Balance at end of period	0	0	0	0
Foreign currency translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	0	(2)	0	(2)
Total Other comprehensive (loss) income, net of tax	0	0	0	0
Balance at end of period	0	(2)	0	(2)
Available-for-sale securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	0	0	0	0
Total Other comprehensive (loss) income, net of tax	0	0	0	0
Balance at end of period	0	0	0	0
Cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	0	0	0	0
Other comprehensive income (loss), before reclassifications, before tax	0	0	0	0
Tax benefit (expense)	0	0	0	0
Total Other comprehensive (loss) income before reclassifications, net of tax	0	0	0	0
Reclassification from accumulated other comprehensive income, before tax	0	0	0	0
Tax (expense) benefit	0	0	0	0
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0	0	0	0
Total Other comprehensive (loss) income, net of tax	0	0	0	0
Balance at end of period	$ 0	$ 0	$ 0	$ 0

Receivables (Details)		6 Months Ended		12 Months Ended
Receivables (Details)	Mar. 30, 2012 USD ($)	Jun. 30, 2018 USD ($) agreement	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Schedule Of Financial Receivables [Line Items]
Number of arrangement with different financial institution to sell customer receivables \| agreement		3
Funding of customer receivables sold		$ 0
Sale of customer receivables	$ 304,000,000
Cash received for receivables	50,000,000	420,000,000	$ 285,000,000
Deferred purchase program receivable	$ 254,000,000	313,000,000		$ 187,000,000
Net cash funding received during the period		300,000,000
Amount of cash draws under arrangement during the period		2,658,000,000
Amount of cash repayments under arrangement during the period		(2,358,000,000)
Amount of cash draws under arrangement since inception		(300,000,000)
Amount of cash repayments under arrangement since inception		300,000,000
Cash outflow from deferred purchase receivable		38,547,000,000
Cash collections of other receivables		(37,885,000,000)
Minimum
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold		200,000,000
Maximum
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold		$ 400,000,000

Inventories - Schedule of Inventory Components (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Finished goods	$ 682	$ 669
Work-in-process	1,485	1,349
Purchased raw materials	401	381
Operating supplies	91	81
Total inventories	$ 2,659	$ 2,480

Inventories - Additional Information (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventories valued on a LIFO basis	$ 1,372	$ 1,208
Total inventories valued on an average-cost basis	527	$ 481
EP&S
Segment Reporting Information [Line Items]
Inventory adjustments	$ 23

Property, Plants, and Equipment, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Less: accumulated depreciation and amortization	$ 6,674	$ 6,392
Properties, plants, and equipment, net	5,582	5,594
Undiscounted cash flows, effect of one percentage point decrease on net cash flows	$ 6
Disks Business
Property, Plant and Equipment [Line Items]
Estimated undiscounted cash flows in excess its carrying value, percent	13.00%
Arconic Engines
Property, Plant and Equipment [Line Items]
Long-lived assets	$ 515
Land and land rights
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	139	140
Structures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,376	2,395
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,148	8,830
Depreciable Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,663	11,365
Properties, plants, and equipment, net	4,989	4,973
Construction in Progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 593	$ 621

Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Millions	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt	$ 6,315		$ 6,807
Other	(15)		(23)
Less: amount due within one year	3		1
Long-term debt, excluding amount due within one year	6,312		6,806
5.72% Notes, due 2019
Debt Instrument [Line Items]
Long-term debt	$ 0		500
Long-term debt, interest rate	5.72%	5.72%
1.63% Convertible Notes, due 2019
Debt Instrument [Line Items]
Long-term debt	$ 403		403
Long-term debt, interest rate	1.63%
6.150% Notes, due 2020
Debt Instrument [Line Items]
Long-term debt	$ 1,000		1,000
Long-term debt, interest rate	6.15%
5.40% Notes due 2021
Debt Instrument [Line Items]
Long-term debt	$ 1,250		1,250
Long-term debt, interest rate	5.40%
5.87% Notes, due 2022
Debt Instrument [Line Items]
Long-term debt	$ 627		627
Long-term debt, interest rate	5.87%
5.125% Notes, due 2024
Debt Instrument [Line Items]
Long-term debt	$ 1,250		1,250
Long-term debt, interest rate	5.125%
5.90% Notes, due 2027
Debt Instrument [Line Items]
Long-term debt	$ 625		625
Long-term debt, interest rate	5.90%
6.75% Bonds, due 2028
Debt Instrument [Line Items]
Long-term debt	$ 300		300
Long-term debt, interest rate	6.75%
5.95% Notes, due 2037
Debt Instrument [Line Items]
Long-term debt	$ 625		625
Long-term debt, interest rate	5.95%
Iowa Finance Authority Loan, due 2042
Debt Instrument [Line Items]
Long-term debt	$ 250		$ 250

Debt - Additional Information (Details) - USD ($)	3 Months Ended			6 Months Ended
Debt - Additional Information (Details) - USD ($)	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Interest expense for premium paid for early redemption of notes in excess of carrying value	$ 89,000,000		$ 183,000,000	$ 203,000,000	$ 298,000,000
5.72% Notes, due 2019
Debt Instrument [Line Items]
Long-term debt, interest rate	5.72%	5.72%		5.72%
Long-term debt						$ 500,000,000
Redemption amount		$ 518,000,000
Loss on prepayment of debt redemption		$ 19,000,000

Debt - Credit Facilities (Details)			3 Months Ended	6 Months Ended
Debt - Credit Facilities (Details)	Jun. 29, 2018 USD ($) extension	Jul. 25, 2014 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 715,000,000	$ 715,000,000
Parent Company
Debt Instrument [Line Items]
Borrowings from credit facility				300,000,000
Repayments of borrowings				$ (300,000,000)
Weighted average interest rate outstanding borrowings			3.30%	3.20%
Debt weighted average maturity term			70 days	65 days
Maximum
Debt Instrument [Line Items]
Applicable margin on LIBOR loans	1.50%
Minimum
Debt Instrument [Line Items]
Applicable margin on LIBOR loans	0.50%
Revolving Credit Agreement
Debt Instrument [Line Items]
Line of credit facility term		5 years
Long-term line of credit			$ 0	$ 0	$ 0
Outstanding amount			0	0	$ 0
Revolving Credit Agreement \| Maximum
Debt Instrument [Line Items]
Commitment fee percentage	0.25%
Revolving Credit Agreement \| Prior To Amendment
Debt Instrument [Line Items]
Long-term line of credit		$ 4,000,000,000
Revolving Credit Agreement \| After Amendment
Debt Instrument [Line Items]
Long-term line of credit	$ 3,000,000,000					$ 3,000,000,000
Maximum increase in borrowing capacity	$ 500,000,000
Debt covenants net leverage ratio	4.50%
Debt covenants net leverage ratio after year three	4.00%
Debt covenants net leverage ratio after year four	3.50%
Number of extensions \| extension	2
Extended additional maturity period	1 year
Minimum indebtedness for other principal amounts	$ 100,000,000
Revolving Credit Agreement \| After Amendment \| Letter of Credit
Debt Instrument [Line Items]
Long-term line of credit	$ 1,000,000,000
Expected Maturity Date Year 2018
Debt Instrument [Line Items]
Outstanding amount			350,000,000	350,000,000
Expected Maturity Date Year 2019
Debt Instrument [Line Items]
Outstanding amount			$ 365,000,000	$ 365,000,000

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Carrying Value
Derivative [Line Items]
Long-term debt, less amount due within one year	$ 6,312	$ 6,806
Fair Value
Derivative [Line Items]
Long-term debt, less amount due within one year	$ 6,457	$ 7,443

Acquisitions and Divestitures (Details) $ in Millions		1 Months Ended	3 Months Ended				6 Months Ended
Acquisitions and Divestitures (Details) $ in Millions	Apr. 02, 2018 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) employee	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Business Acquisition [Line Items]
Restructuring and other charges			$ 15		$ 26		$ 22	$ 99
Latin America Extrusions (LAE) \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Business Acquisition [Line Items]
Disposal group, including discontinued operation, revenue					$ 30		$ 25	$ 56
Cash received on sale of operations	$ 5
Latin America Extrusions (LAE) \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Divested Businesses
Business Acquisition [Line Items]
Restructuring and other charges				$ 41
Slim Aluminium
Business Acquisition [Line Items]
Cash expense related to sale of rolling mill		$ 10
Third party guarantee with a fair value related to environmental remediation		$ 5
Disposal group, including discontinued operation, revenue						$ 37
Number of employees \| employee						312
Slim Aluminium \| Restructuring and Other Charges
Business Acquisition [Line Items]
Loss on sale of rolling mill						$ 60

Contingencies and Commitments (Details) € in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 EUR (€)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) location	Jul. 31, 2018 USD ($)	Jul. 31, 2018 EUR (€)	Dec. 31, 2017 USD ($)	Nov. 01, 2016 USD ($)	Jul. 31, 2013 USD ($)	Jul. 31, 2013 EUR (€)
Loss Contingencies [Line Items]
Number of cleanup locations \| location				100
Remediation reserve balance			$ 287	$ 287			$ 294
Remediation reserve balance, classified as a current liability			51	51			41
Payments related to remediation expenses applied against the reserve			5	$ 8
Actual remediation fieldwork period				4 years
Guarantees of third party related to project financing			33	$ 33
Long-term debt			6,315	6,315			6,807
Total amount committed under outstanding surety bonds			49	49
Bank Loan Obligations \| Letter of Credit
Loss Contingencies [Line Items]
Long-term debt			128	128
Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing			111	111			197
Total amount committed under outstanding surety bonds			25	25
Other Noncurrent Liabilities and Deferred Credits
Loss Contingencies [Line Items]
Combined fair value of guarantees			7	7			8
Subsequent Event
Loss Contingencies [Line Items]
Income tax examination assessment outstanding					$ 175	€ 152
Massena West, NY
Loss Contingencies [Line Items]
Remediation reserve balance			$ 211	$ 211			215
Spain
Loss Contingencies [Line Items]
Income tax examination assessment, including interest									$ 151	€ 131
Spain \| Forecast
Loss Contingencies [Line Items]
Potential impact to provision for income taxes	$ 59	€ 51
Alcoa Corporation
Loss Contingencies [Line Items]
Tax agreement, indemnification of ultimate liability, percent			49.00%	49.00%
Alcoa Corporation \| Forecast
Loss Contingencies [Line Items]
Tax agreement, indemnification of ultimate liability, percent	49.00%	49.00%
Recurring Costs of Managing Hazardous Substances and Environmental Programs \| Maximum
Loss Contingencies [Line Items]
Percentage of cost of goods sold				1.00%
Supply Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing			$ 1,156	$ 1,156			$ 1,297
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount committed								$ 53

Subsequent Events (Details) $ in Millions	12 Months Ended
Subsequent Events (Details) $ in Millions	Dec. 31, 2017 USD ($)
Building and Construction Systems
Subsequent Event [Line Items]
Third-party sales	$ 1,070