Howmet Aerospace (HWM) 10-Q 1 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 29, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
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		448,629,078
Entity Small Business	false
Entity Emerging Growth Company	false

Statement of Consolidated Opera

Statement of Consolidated Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Sales (C)	$ 3,541	$ 3,445
Cost of goods sold (exclusive of expenses below)	2,818	2,768
Selling, general administrative, and other expenses	178	172
Research and development expenses	22	23
Provision for depreciation and amortization	137	142
Restructuring and other charges (D)	12	7
Operating income	374	333
Interest expense	85	114
Other expense, net (E)	32	20
Income before income taxes	257	199
Provision for income taxes (G)	70	56
Net income	187	143
Amounts Attributable to Arconic Common Shareholders (I):
Net income	$ 186	$ 142
Earnings per share - basic (in usd per share)	$ 0.40	$ 0.30
Earnings per share - diluted (in usd per share)	$ 0.39	$ 0.29
Average Shares Outstanding (I):
Average shares outstanding - basic (in shares)	471	482
Average shares outstanding - diluted (in shares)	489	503

Statement of Consolidated Compr

Statement of Consolidated Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net income	$ 187	$ 143
Other comprehensive income, net of tax (J):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	40	143
Foreign currency translation adjustments	26	122
Net change in unrealized gains on available-for-sale securities	3	0
Net change in unrecognized losses/gains on cash flow hedges	7	(7)
Total Other comprehensive income, net of tax	76	258
Comprehensive income	263	401
Arconic
Net income	187	143
Other comprehensive income, net of tax (J):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	40	143
Foreign currency translation adjustments	26	122
Net change in unrealized gains on available-for-sale securities	3	0
Net change in unrecognized losses/gains on cash flow hedges	7	(7)
Total Other comprehensive income, net of tax	76	258
Comprehensive income	263	401
Noncontrolling Interests
Net income	0	0
Other comprehensive 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
Foreign currency translation adjustments	0	0
Net change in unrealized gains on available-for-sale securities	0	0
Net change in unrecognized losses/gains on cash flow hedges	0	0
Total Other comprehensive income, net of tax	0	0
Comprehensive income	$ 0	$ 0

Consolidated Balance Sheet (una

Consolidated Balance Sheet (unaudited) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 1,319	$ 2,277
Receivables from customers, less allowances of $4 in 2019 and 2018 (K)	1,170	1,047
Other receivables (K)	646	451
Inventories (L)	2,612	2,492
Prepaid expenses and other current assets	306	314
Total current assets	6,053	6,581
Properties, plants, and equipment, net (M)	5,727	5,704
Goodwill (C)	4,509	4,500
Deferred income taxes	480	573
Intangibles, net	912	919
Other noncurrent assets (N)	680	416
Total assets	18,361	18,693
Current liabilities:
Accounts payable, trade	2,193	2,129
Accrued compensation and retirement costs	339	370
Taxes, including income taxes	114	118
Accrued interest payable	97	113
Other current liabilities (N)	481	356
Short-term debt	435	434
Total current liabilities	3,659	3,520
Long-term debt, less amount due within one year (O and P)	5,899	5,896
Accrued pension benefits (F)	2,172	2,230
Accrued other postretirement benefits (F)	636	723
Other noncurrent liabilities and deferred credits (B and N)	817	739
Total liabilities	13,183	13,108
Contingencies and commitments (R)
Arconic shareholders’ equity:
Preferred stock	55	55
Common stock	453	483
Additional capital	7,644	8,319
Accumulated deficit	(134)	(358)
Accumulated other comprehensive loss (J)	(2,852)	(2,926)
Total Arconic shareholders’ equity	5,166	5,573
Noncontrolling interests	12	12
Total equity	5,178	5,585
Total liabilities and equity	$ 18,361	$ 18,693

Consolidated Balance Sheet (u_2

Consolidated Balance Sheet (unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable, current	$ 4	$ 4

Statement of Consolidated Cash

Statement of Consolidated Cash Flows (unaudited) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Operating activities
Net income	$ 187	$ 143
Adjustments to reconcile net income to cash used for operations:
Depreciation and amortization	137	142
Deferred income taxes	8	18
Restructuring and other charges	12	7
Net loss from investing activities - asset sales	2	3
Net periodic pension benefit cost (F)	29	41
Stock-based compensation	10	15
Other	11	49
Changes in assets and liabilities, excluding effects of acquisitions, divestitures, and foreign currency translation adjustments:
(Increase) in receivables	(489)	(403)
(Increase) in inventories	(118)	(141)
(Increase) in prepaid expenses and other current assets	(14)	(12)
Increase in accounts payable, trade	65	14
(Decrease) in accrued expenses	(69)	(118)
Increase in taxes, including income taxes	47	8
Pension contributions	(55)	(177)
(Increase) decrease in noncurrent assets	(1)	1
(Decrease) in noncurrent liabilities	(20)	(26)
Cash used for operations	(258)	(436)
Financing Activities
Net change in short-term borrowings (original maturities of three months or less)	1	5
Additions to debt (original maturities greater than three months)	150	150
Payments on debt (original maturities greater than three months)	(151)	(651)
Premiums paid on early redemption of debt	0	(17)
Proceeds from exercise of employee stock options	1	12
Dividends paid to shareholders	(29)	(30)
Repurchase of common stock (H)	(700)	0
Other	(13)	(11)
Cash used for financing activities	(741)	(542)
Investing Activities
Capital expenditures	(168)	(117)
Proceeds from the sale of assets and businesses	4	0
Sales of investments	47	9
Cash receipts from sold receivables (K)	160	136
Other	(1)	1
Cash provided from investing activities	42	29
Effect of exchange rate changes on cash, cash equivalents and restricted cash	1	4
Net change in cash, cash equivalents and restricted cash	(956)	(945)
Cash, cash equivalents and restricted cash at beginning of year	2,282	2,153	$ 2,153
Cash, cash equivalents and restricted cash at end of period	$ 1,326	$ 1,208	$ 2,282

Statement of Changes in Consoli

Statement of Changes in Consolidated Equity (unaudited) - USD ($) $ in Millions	Total	Preferred Class A	Preferred stock	Common stock	Additional capital	Accumulated deficit	Accumulated deficitPreferred Class A	Accumulated other comprehensive loss	Noncontrolling Interests
Balance at beginning of period at Dec. 31, 2017	$ 4,924		$ 55	$ 481	$ 8,266	$ (1,248)		$ (2,644)	$ 14
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	143					143			0
Other comprehensive income (J)	258							258	0
Cash dividends declared:
Preferred dividends declared, value		$ (1)					$ (1)
Common share, value	(58)					(58)
Stock-based compensation	15				15
Common stock issued: compensation plans	1			2	(1)
Balance at end of period at Mar. 31, 2018	5,282		55	483	8,280	(1,164)		(2,386)	14
Balance at beginning of period at Dec. 31, 2017	4,924		55	481	8,266	(1,248)		(2,644)	14
Cash dividends declared:
Other	1					1
Balance at end of period at Dec. 31, 2018	5,585		55	483	8,319	(358)		(2,926)	12
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	187					187			0
Other comprehensive income (J)	76							76	0
Cash dividends declared:
Preferred dividends declared, value		$ (1)					$ (1)
Common share, value	(38)					(38)
Repurchase and retirement of common stock (H)	(700)			(32)	(668)
Stock-based compensation	8				8
Common stock issued: compensation plans	(13)			2	(15)
Balance at end of period at Mar. 31, 2019	$ 5,178		$ 55	$ 453	$ 7,644	$ (134)		$ (2,852)	$ 12

Statement of Changes in Conso_2

Statement of Changes in Consolidated Equity (unaudited) (Parenthetical) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Common stock, dividends per share (in usd per share)	$ 0.08	$ 0.12
Preferred Class A
Preferred, dividends per share (in usd per share)	$ 0.9375	$ 0.9375

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2019
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 2018 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, 2018 , which includes all disclosures required by GAAP. Certain amounts in previously issued financial statements were reclassified to conform to the current period presentation (see Note C ).

Recently Adopted and Recently I

Recently Adopted and Recently Issued Accounting Guidance	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Recently Adopted and Recently Issued Accounting Guidance	Recently Adopted and Recently Issued Accounting Guidance Adopted In February 2016, the Financial Accounting Standards Board (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, initially measured at the present value of the future lease payments for all operating leases with a term greater than 12 months. These changes became effective for Arconic on January 1, 2019 and have been applied using the modified retrospective approach as of the date of adoption, under which leases existing at, or entered into after, January 1, 2019 were required to be recognized and measured. Prior period amounts have not been adjusted and continue to be reflected in accordance with the Company’s historical accounting. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company to carry forward the historical lease classification. The Company also elected to separate lease components from non-lease components for all classes of assets. The adoption of this new standard resulted in the Company recording operating lease right-of-use assets and lease liabilities of approximately $320 on the Consolidated Balance Sheet as of January 1, 2019. Also, the Company reclassified cash proceeds of $119 from Other noncurrent liabilities and deferred credits, assets of $24 from Properties, plants, and equipment, net, and deferred tax assets of $22 from Other noncurrent assets to Accumulated deficit reflecting the cumulative effect of an accounting change related to the sale-leaseback of the Texarkana, Texas cast house (see Note Q ). The adoption of the standard had no impact on the Statement of Consolidated Operations or Statement of Consolidated Cash Flows. In August 2017, the FASB issued guidance that made more financial and nonfinancial hedging strategies eligible for hedge accounting. It also amended the presentation and disclosure requirements and changed 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 became effective for Arconic on January 1, 2019. For cash flow hedges, Arconic recorded a cumulative effect adjustment of $2 related to eliminating the separate measurement of ineffectiveness by decreasing Accumulated other comprehensive loss and increasing Accumulated deficit on the accompanying Consolidated Balance Sheet. The amendments to presentation and disclosure are required prospectively. Arconic has determined that under the new accounting guidance it will be able to more broadly use cash flow hedge accounting for its variable priced inventory purchases and customer sales. Issued 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 2018, the FASB issued guidance that impacts disclosures for defined benefit pension plans and other postretirement benefit plans. These changes become effective for Arconic's annual report for the year ending December 31, 2020, with early adoption permitted. Management has determined that the adoption of this guidance will not have a material impact on the Consolidated Financial Statements.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Segment Information	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 2019, management transferred its aluminum extrusions operations (Aluminum Extrusions) from the Arconic Engineered Structures (AES) business unit within the Engineered Products and Solutions (EP&S) segment to the Global Rolled Products (GRP) segment, based on synergies with GRP including similar customer base, technologies, and manufacturing capabilities. Prior period financial information has been recast to conform to current year presentation. 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. Segment operating profit includes 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. Differences between segment totals and consolidated Arconic are in Corporate. As a result of the reorganization of the business noted above, management assessed and concluded that the remaining AES business unit within the EP&S segment and the Aluminum Extrusions business unit within the GRP segment represent reporting units for purposes of evaluating goodwill for impairment. Goodwill of approximately $110 was reallocated from the AES reporting unit to the Aluminum Extrusions reporting unit and these reporting units were evaluated for impairment during the first quarter of 2019. The estimated fair value of each of these reporting units substantially exceeded their carrying value; thus, there was no goodwill impairment. The Company will continue to evaluate its organizational structure and portfolio in conjunction with its planned separation (see Note S ), which may result in further changes to its reportable segments and the need to evaluate assets for impairment in future periods. The operating results of Arconic’s reportable segments were as follows: Engineered Products and Solutions Global Rolled Products Transportation and Construction Solutions Total Segment First quarter ended March 31, 2019 Sales: Third-party sales $ 1,502 $ 1,503 $ 535 $ 3,540 Intersegment sales — 55 — 55 Total sales $ 1,502 $ 1,558 $ 535 $ 3,595 Profit and loss: Segment operating profit $ 253 $ 107 $ 87 $ 447 Restructuring and other charges 14 6 9 29 Provision for depreciation and amortization 64 54 13 131 First quarter ended March 31, 2018 Sales: Third-party sales $ 1,426 $ 1,481 $ 537 $ 3,444 Intersegment sales — 57 — 57 Total sales $ 1,426 $ 1,538 $ 537 $ 3,501 Profit and loss: Segment operating profit $ 209 $ 124 $ 67 $ 400 Restructuring and other charges 1 (1 ) — — Provision for depreciation and amortization 65 56 13 134 The following table reconciles Total segment operating profit to Consolidated income before income taxes : First quarter ended March 31, 2019 2018 Total segment operating profit $ 447 $ 400 Unallocated amounts: Restructuring and other charges (12 ) (7 ) Corporate expense (61 ) (60 ) Consolidated operating income $ 374 $ 333 Interest expense (85 ) (114 ) Other expense, net (32 ) (20 ) Consolidated income before income taxes $ 257 $ 199 The total assets of Arconic's reportable segment were as follows: March 31, 2019 December 31, 2018 Engineered Products and Solutions $ 10,153 $ 9,797 Global Rolled Products 4,768 4,486 Transportation and Construction Solutions 1,206 1,089 Total segment assets $ 16,127 $ 15,372 Segment assets at March 31, 2019 included operating lease right-of-use assets (see Notes B and N ). The following table reconciles Total segment assets to Consolidated assets : March 31, 2019 December 31, 2018 Total segment assets $ 16,127 $ 15,372 Unallocated amounts: Cash and cash equivalents 1,319 2,277 Deferred income taxes 480 573 Corporate fixed assets, net 308 305 Fair value of derivative contracts 8 37 Other 119 129 Consolidated assets $ 18,361 $ 18,693 The following table disaggregates revenue by major end market served. Differences between segment totals and consolidated Arconic are in Corporate: Engineered Products and Solutions Global Rolled Products Transportation and Construction Solutions Total Segment First quarter ended March 31, 2019 Aerospace $ 1,250 $ 302 $ — $ 1,552 Transportation 87 649 255 991 Building and construction — 49 281 330 Industrial and Other 165 503 (1 ) 667 Total end-market revenue $ 1,502 $ 1,503 $ 535 $ 3,540 First quarter ended March 31, 2018 Aerospace $ 1,141 $ 248 $ — $ 1,389 Transportation 73 622 243 938 Building and construction — 48 285 333 Industrial and Other 212 563 9 784 Total end-market revenue $ 1,426 $ 1,481 $ 537 $ 3,444

Restructuring and Other Charges

Restructuring and Other Charges	3 Months Ended
	Mar. 31, 2019
Restructuring and Related Activities [Abstract]
Restructuring and Other Charges	Restructuring and Other Charges In the first quarter of 2019, Arconic recorded Restructuring and other charges of $12 ( $10 after-tax), which included $65 ( $51 after-tax) for layoff costs, including the separation of approximately 800 employees ( 425 in Corporate, 168 in the Engineered Products and Solutions segment, 121 in the Transportation and Construction Solutions segment, and 86 in the Global Rolled Products segment); a $2 ( $1 after-tax) net charge for executive severance net of the benefit of forfeited executive stock compensation; a pension settlement charge of $2 ( $2 after-tax); and $1 ( $1 after-tax) for other miscellaneous items; offset by a benefit of $58 ( $45 after-tax) related to the elimination of life insurance benefits for U.S. salaried and non-bargained hourly retirees of the Company and its subsidiaries. In the first quarter of 2018, Arconic recorded Restructuring and other charges of $7 ( $5 after-tax), which included $5 ( $4 after-tax) for pension curtailment charges; $4 ( $3 after-tax) for layoff costs, including the separation of approximately 16 employees (all in Corporate); a charge of $2 ( $1 after-tax) for other miscellaneous items; and a benefit of $4 ( $3 after-tax) for the reversal of a number of small layoff reserves related to prior periods. As of March 31, 2019 , approximately 247 of the 800 employees associated with 2019 restructuring programs, approximately 115 of the 125 employees associated with 2018 restructuring programs, and approximately 570 of the 660 employees associated with 2017 restructuring programs were separated. Most of the remaining separations for the 2019 restructuring programs and all of the remaining separations for the 2018 and 2017 restructuring programs, are expected to be completed by the end of 2019. For the first quarter of 2019 , cash payments of $7 , $3 , and $4 were made against the layoff reserves related to the 2019 , 2018 , and 2017 restructuring programs, respectively. Activity and reserve balances for restructuring and other charges were as follows: Layoff costs Other exit costs Total Reserve balances at December 31, 2017 $ 56 $ 2 $ 58 Cash payments (47 ) (2 ) (49 ) Restructuring charges 111 13 124 Other (1) (110 ) 2 (108 ) Reserve balances at December 31, 2018 10 15 25 Cash payments (14 ) (3 ) (17 ) Restructuring charges 11 — 11 Other (1) 57 (9 ) 48 Reserve balances at March 31, 2019 $ 64 $ 3 $ 67 (1) Other includes adjustments of previously recorded restructuring charges and credits, and the effects of foreign currency translation. In 2019, Other for layoff costs included reclassifications of a $58 credit for elimination of life insurance benefits for U.S. salaried and non-bargaining hourly retirees and a $2 pension settlement charge, as the impacts were reflected in Arconic's separate liabilities for Accrued pension benefits and Accrued postretirement benefits. Other for other exit costs included a reclassification of $9 in lease exit costs to right-of-use assets within Other noncurrent assets in accordance with the new lease accounting standard. In 2018, Other for layoff costs included reclassifications of $119 in pension costs and a $28 credit in postretirement benefits, as the impacts were reflected in Arconic's separate liabilities for Accrued pension benefits and Accrued postretirement benefits, and reversals of previously recorded restructuring charges of $19 . The remaining reserves are expected to be paid in cash during 2019, with the exception of approximately $3 , which is expected to be paid in 2020 related to severance payments.

Other Expense, Net

Other Expense, Net	3 Months Ended
	Mar. 31, 2019
Other Income and Expenses [Abstract]
Other Expense, Net	Other Expense, Net First quarter ended March 31, 2019 2018 Non-service related net periodic benefit cost $ 29 $ 28 Interest income (10 ) (6 ) Foreign currency gains, net — (3 ) Net loss from asset sales 2 3 Other, net 11 (2 ) $ 32 $ 20

Pension and Other Postretiremen

Pension and Other Postretirement Benefits	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits	Pension and Other Postretirement Benefits The components of net periodic benefit cost were as follows: First quarter ended March 31, 2019 2018 Pension benefits Service cost $ 7 $ 20 Interest cost 59 55 Expected return on plan assets (72 ) (77 ) Recognized net actuarial loss 35 42 Amortization of prior service cost (benefit) — 1 Settlements 2 — Curtailments — 5 Net periodic benefit cost (1) $ 31 $ 46 Other postretirement benefits Service cost $ 2 $ 2 Interest cost 7 7 Recognized net actuarial loss 1 2 Amortization of prior service cost (benefit) (1 ) (2 ) Curtailments (58 ) — Net periodic benefit cost (1) $ (49 ) $ 9 (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, net in the Statement of Consolidated Operations. In the first quarter of 2019, the Company communicated to plan participants that, effective May 1, 2019, it will eliminate the life insurance benefit for its U.S. salaried and non-bargained hourly retirees of the Company and its subsidiaries. As a result of this change, in the first quarter of 2019, the Company recorded a decrease to the Accrued other postretirement benefits liability of $63 which was offset by a curtailment benefit of $58 in Restructuring and other charges and $5 in Accumulated other comprehensive loss. Additionally, in the first quarter of 2019, the Company communicated to plan participants that, effective December 31, 2019, it will eliminate certain health care subsidies for its U.S. salaried and non-bargained hourly retirees of the Company and its subsidiaries. As a result of this change, in the first quarter of 2019, the Company recorded a decrease to the Accrued other postretirement benefits liability of $12 which was offset in Accumulated other comprehensive loss. In the first quarter of 2019, the Company applied settlement accounting to a U.S. pension plan due to lump sum payments to participants which resulted in a settlement charge of $2 that was recorded in Restructuring and other charges. On 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. During the third quarter of 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 stipulated that Arconic make cash contributions of $150 over a period of 30 months (from November 1, 2016) to its two largest pension plans. The Company satisfied the requirements of the plan by making payments of $34 , $66 , and $50 in April 2019, March 2018, and April 2017, respectively.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	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 first quarter of 2019 and 2018, the estimated annual effective tax rate, before discrete items, applied to ordinary income was 25.9% and 26.5% , respectively. The rate in each period was higher than the U.S. federal statutory rate of 21% primarily due to additional estimated U.S. tax on Global Intangible Low-Taxed Income, domestic taxable income in certain U.S. states no longer subject to valuation allowance, and foreign income taxed in higher rate jurisdictions. For the first quarter of 2019 and 2018, the tax rate including discrete items was 27.2% and 28.1% , respectively and included a discrete charge of $1 related to other items in the first quarter of 2019 and a discrete tax charge of $2 related to stock compensation in the first quarter of 2018. The tax provisions for the first quarter of 2019 and 2018 were comprised of the following: First quarter ended March 31, 2019 2018 Pre-tax income at estimated annual effective income tax rate before discrete items $ 67 $ 53 Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized 2 1 Other discrete items 1 2 Provision for income taxes $ 70 $ 56

Common Stock

Common Stock	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Common Stock	Common Stock On February 19, 2019, the Company entered into an accelerated share repurchase (ASR) agreement with JPMorgan Chase Bank to repurchase $700 of its common stock, pursuant to the share repurchase programs previously authorized by its Board of Directors (the Board). Under the ASR agreement, Arconic received an initial delivery of 31,908,831 shares on February 21, 2019, which were immediately retired. On April 25, 2019, the ASR concluded with the Company receiving 4,525,592 additional shares on April 29, 2019, which were immediately retired. A total of 36,434,423 shares, at an average price of $ 19.21 per share, were repurchased under the agreement. As of April 29, 2019, there were 448,629,078 shares of common stock outstanding. After giving effect to the ASR, $300 remains available under the prior authorizations by the Board for share repurchases through the end of 2020.

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Earnings Per Share	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): First quarter ended March 31, 2019 2018 Net income $ 187 $ 143 Less: preferred stock dividends declared (1 ) (1 ) Net income available to Arconic common shareholders - basic 186 142 Add: Interest expense related to convertible notes 4 3 Net income available to Arconic common shareholders - diluted $ 190 $ 145 Average shares outstanding - basic 471 482 Effect of dilutive securities: Stock options — 5 Stock and performance awards 4 2 Convertible notes 14 14 Average shares outstanding - diluted 489 503 Common stock outstanding at March 31, 2019 and 2018 was 453 and 483 , respectively. The decrease in common stock outstanding at March 31, 2019 was due to the impact of share repurchases of approximately 32 in the first quarter of 2019 (see Note H ). As average shares outstanding are used in the calculation for both basic and diluted EPS, the full impact of share repurchases was not realized in the first quarter of 2019 EPS as the share repurchases occurred midway through the quarter on February 21, 2019. The following shares were excluded from the calculation of average shares outstanding – diluted as their effect was anti-dilutive (shares in millions). First quarter ended March 31, 2019 2018 Stock options (1) 8 6 (1) The average exercise price per share of options was $26.67 and $30.75 for the first quarter of 2019 and 2018 , respectively.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Accumulated Other Comprehensive Loss	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: First quarter ended March 31, 2019 2018 Pension and other postretirement benefits ( F ) Balance at beginning of period $ (2,344 ) $ (2,230 ) Other comprehensive income: Unrecognized net actuarial loss and prior service cost/benefit 72 137 Tax expense (16 ) (31 ) Total Other comprehensive income before reclassifications, net of tax 56 106 Amortization of net actuarial loss and prior service cost (1) (21 ) 48 Tax benefit (expense) (2) 5 (11 ) Total amount reclassified from Accumulated other comprehensive loss, net of tax (5) (16 ) 37 Total Other comprehensive income 40 143 Balance at end of period $ (2,304 ) $ (2,087 ) Foreign currency translation Balance at beginning of period $ (583 ) $ (437 ) Other comprehensive income (3) 26 122 Balance at end of period $ (557 ) $ (315 ) Available-for-sale securities Balance at beginning of period $ (3 ) $ (2 ) Other comprehensive income (4) 3 — Balance at end of period $ — $ (2 ) Cash flow hedges Balance at beginning of period $ 4 $ 25 Adoption of accounting standards (B) (2 ) — Other comprehensive income (loss): Net change from periodic revaluations 8 (6 ) Tax (expense) benefit (1 ) 1 Total Other comprehensive income (loss) before reclassifications, net of tax 7 (5 ) Net amount reclassified to earnings — (3 ) Tax benefit (2) — 1 Total amount reclassified from Accumulated other comprehensive income, net of tax (5) — (2 ) Total Other comprehensive income (loss) 7 (7 ) Balance at end of period $ 9 $ 18 Total balance at end of period $ (2,852 ) $ (2,386 ) (1) These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note F ). (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, 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

Receivables	3 Months Ended
	Mar. 31, 2019
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 up to a maximum funding 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 ( $3,108 in draws and $2,808 in repayments) since the program’s inception, including net cash draws totaling $0 ( $150 in draws and $150 in repayments) for the first quarter of 2019 . As of March 31, 2019 and December 31, 2018 , the deferred purchase program receivable was $430 and $234 , 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 $43,899 and $43,190 , 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

Inventories	3 Months Ended
	Mar. 31, 2019
Inventory Disclosure [Abstract]
Inventories	Inventories March 31, 2019 December 31, 2018 Finished goods $ 699 $ 668 Work-in-process 1,448 1,371 Purchased raw materials 371 366 Operating supplies 94 87 Total inventories $ 2,612 $ 2,492 At March 31, 2019 and December 31, 2018 , the portion of inventories valued on a last-in, first-out (LIFO) basis was $1,340 and $1,292 , respectively. If valued on an average-cost basis, total inventories would have been $527 and $530 higher at March 31, 2019 and December 31, 2018 , respectively.

Property, Plants, and Equipment

Property, Plants, and Equipment, Net	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Properties, Plants, and Equipment, Net	Properties, Plants, and Equipment, Net March 31, 2019 December 31, 2018 Land and land rights $ 137 $ 136 Structures 2,357 2,364 Machinery and equipment: 9,267 9,234 11,761 11,734 Less: accumulated depreciation and amortization 6,811 6,769 4,950 4,965 Construction work-in-progress 777 739 $ 5,727 $ 5,704

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	Leases The Company determines whether or not a contract contains a lease at inception. The Company leases land and buildings, plant equipment, vehicles, and computer equipment which have been classified as operating leases. Certain real estate leases include one or more options to renew; the exercise of lease renewal options is at the Company’s discretion. The Company includes renewal option periods in the lease term when it is determined that the options are reasonably certain to be exercised. Certain of Arconic's real estate lease agreements include rental payments that either have fixed contractual increases over time or adjust periodically for inflation. Certain of the Company's lease agreements include variable lease payments. The variable portion of payments is not included in the initial measurement of the right-of-use asset or lease liability due to the uncertainty of the payment amount and is recorded as lease cost in the period incurred. The Company also rents or subleases certain real estate to third parties, which is not material to the consolidated financial statements. Operating lease right-of-use assets and lease liabilities with an initial term greater than 12 months are recorded on the balance sheet at the present value of the future minimum lease payments over the lease term at the lease commencement date and are recognized as lease expense on a straight-line basis over the lease term. The Company uses an incremental collateralized borrowing rate based on the information available at the lease commencement date in determining the present value of future payments, as most of its leases do not provide an implicit rate. The operating lease right-of-use assets also include any lease prepayments made and were reduced by lease incentives and accrued exit costs as of the adoption date. Operating lease cost, which includes short-term leases and variable lease payments and approximates cash paid, was $37 and $38 in the first quarter ended March 31, 2019 and 2018 , respectively. Operating lease right-of-use assets and lease liabilities in the Consolidated Balance Sheet were as follows: March 31, 2019 Right-of-use assets classified in Other noncurrent assets $ 302 Current portion of lease liabilities classified in Other current liabilities 94 Long-term portion of lease liabilities classified in Other noncurrent liabilities and deferred credits 215 Total lease liabilities $ 309 Future minimum contractual operating lease obligations were as follows: March 31, 2019 December 31, 2018 2019 $ 75 $ 94 2020 79 74 2021 59 54 2022 43 40 2023 31 30 Thereafter 91 87 Total lease payments $ 378 $ 379 Less: Imputed interest (69 ) Present value of lease liabilities $ 309 Right-of-use assets obtained in exchange for operating lease obligations in the first quarter ended March 31, 2019 was $6 . The weighted-average remaining lease term and weighted-average discount rate at March 31, 2019 was 6 years and 6.2% , respectively.

Debt

Debt	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Debt	Debt March 31, 2019 December 31, 2018 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) (26 ) (29 ) 6,304 6,301 Less: amount due within one year 405 405 Total long-term debt $ 5,899 $ 5,896 (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. Credit Facilities. Arconic maintains a Five-Year Revolving Credit Agreement (the “Credit Agreement”) with a syndicate of lenders and issuers named therein that matures on June 29, 2023 and provides for a senior unsecured revolving credit facility of $3,000 . There were no amounts outstanding at March 31, 2019 or December 31, 2018 , and no amounts were borrowed during 2019 or 2018 under the Credit Agreement. In addition to the Credit Agreement, Arconic has a number of other credit agreements that provide a combined borrowing capacity of $715 as of March 31, 2019 , of which $465 is due to expire in 2019 and $250 is due to expire in 2020 . 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 three months ended March 31, 2019 , Arconic borrowed and repaid $150 and $150 , respectively, under these other credit facilities. The weighted-average interest rate and weighted-average days outstanding during the first quarter of 2019 were 3.9% and 14 days, respectively.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	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 their fair values. The Company holds exchange-traded fixed income securities which are considered available-for-sale securities that are carried at fair value which is based on quoted market prices which are classified in Level 1 of the fair value hierarchy. 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. March 31, 2019 December 31, 2018 Carrying value Fair value Carrying value Fair value Long-term debt, less amount due within one year $ 5,899 $ 6,125 $ 5,896 $ 5,873 Restricted cash was $7 and $6 at March 31, 2019 and December 31, 2018 , respectively.

Acquisitions and Divestitures

Acquisitions and Divestitures	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Acquisitions and Divestitures	Acquisitions and Divestitures 2018 Divestitures. On April 2, 2018, Arconic completed the sale of its Latin America extrusions business to a subsidiary of Hydro Extruded Solutions AS for $2 following the settlement of post-closing and other adjustments in December 2018. As a result of entering into the agreement to sell the Latin America extrusions business in December 2017, a charge of $41 was recognized in the fourth quarter of 2017 in Restructuring and other charges in the Statement of Consolidated Operations related to the non-cash impairment of the net book value of the business and an additional charge of $2 related to a post-closing adjustment was recognized in the fourth quarter of 2018. The operating results and assets and liabilities of the business were included in the Transportation and Construction Solutions segment. This business generated sales of $25 in the first quarter of 2018 and had 612 employees at the time of divestiture. 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. In the first quarter of 2019, the Company decided to no longer pursue the sale of BCS and the business continues to be reported in the Transportation and Construction Solutions segment. On October 31, 2018, the Company sold its Texarkana, Texas rolling mill and cast house, which had a combined net book value of $63 , to Ta Chen International, Inc. for $302 in cash, including the settlement of post-closing adjustments, plus additional contingent consideration of up to $50 . The contingent consideration relates to the achievement of various milestones within 36 months of the transaction closing date associated with operationalizing the rolling mill equipment. The operating results and assets and liabilities of the business were included in the Global Rolled Products segment. The Texarkana rolling mill facility had previously been idle since late 2009. In early 2016, the Company restarted the Texarkana cast house to meet demand for aluminum slab. As part of the agreement, the Company will continue to produce aluminum slab at the facility for a period of 18 months through a lease back of the cast house building and equipment, after which time, Ta Chen will perform toll processing of metal for the Company for a period of six months. The Company will supply Ta Chen with cold-rolled aluminum coil during this 24 -month period. The sale of the rolling mill and cast house has been accounted for separately. The gain on the sale of the rolling mill of $154 , including the fair value of contingent consideration of $5 , was recorded in Restructuring and other charges in the Statement of Consolidated Operations in the fourth quarter of 2018. The Company will reevaluate its estimate of the remaining $45 of contingent consideration to which it will be entitled at the end of each reporting period and recognize any changes thereto in the Statement of Consolidated Operations. The Company has continuing involvement related to the lease back of the cast house. As a result, in 2018, the Company continued to treat the cast house building and equipment that it sold to Ta Chen as owned and therefore reflected the following balances in its Consolidated Balance Sheet at December 31, 2018: assets of $24 in Properties, plants, and equipment, net; cash proceeds of $119 in Other noncurrent liabilities and deferred credits (which included a deferred gain of $95 ); and a deferred tax asset of $22 in Other noncurrent assets. In the first quarter of 2019, in conjunction with the adoption of the new lease accounting standard (see Note B ), the Company's continuing involvement no longer requires deferral of the recognition of the cast house sale. As such, the cash proceeds, fixed assets, and deferred tax asset related to the cast house were reclassified to Accumulated deficit as a cumulative effect of an accounting change.

Contingencies and Commitments

Contingencies and Commitments	3 Months Ended
	Mar. 31, 2019
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 $261 at March 31, 2019 and $266 at December 31, 2018 (of which $79 and $81 , 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 $3 in the first quarter of 2019 and 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, 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 March 31, 2019 and December 31, 2018 , the reserve balance associated with this matter was $195 and $198 , respectively. In the first quarter of 2019, Arconic received approval from the EPA of its final remedial design which is now under construction and is expected to be completed in 2022. As the project proceeds, the liability may be updated due to factors such as changes in remedial requirements, site restoration costs, and ongoing operation and maintenance costs, among others. 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. 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 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 $171 ( €152 ), including interest. In March 2019, the Supreme Court of Spain accepted the Company's petition to review the National Court’s decision. The Company will proceed with filing a formal appeal of the assessment with the Supreme Court of Spain, who will review the assessment on its merits and render a final decision. In the event the Company receives an unfavorable ruling from 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. Arconic has an income tax reserve, including interest, of $59 ( €52 ) and an indemnification receivable of $28 ( €25 ), representing Alcoa Corporation’s 49% share of the liability. The reserve and indemnification receivable were established in the third quarter of 2018. 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 As previously reported, on June 13, 2017, the Grenfell Tower in London, UK caught fire resulting in fatalities, injuries and damage. A French subsidiary of Arconic, Arconic Architectural Products SAS (AAP SAS), supplied a product, Reynobond PE, to its customer, a cladding system fabricator, which used the product as one component of the overall cladding system on Grenfell Tower. The fabricator supplied its portion of the cladding system to the façade installer, who then completed and installed the system under the direction of the general contractor. Neither Arconic nor AAP SAS was involved in the design or installation of the system used at the Grenfell Tower, nor did it have a role in any other aspect of the building’s refurbishment or original design. Regulatory investigations into the overall Grenfell Tower matter are being conducted, including a criminal investigation by the London Metro Police, a Public Inquiry by the British government and a consumer protection inquiry by a French public authority. AAP SAS has sought and received core participant status in the Public Inquiry. The Company will no longer sell the PE product for architectural use on buildings. 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 is now closed and the parties await a ruling. Raul v. Albaugh, et al. As previously reported, 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. 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, tax and antitrust 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 March 31, 2019 , 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 2019 and 2026 , was $29 at March 31, 2019 . 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 $6 at March 31, 2019 and December 31, 2018 , respectively, and were included in Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet. Arconic was required to provide a guarantee up to an estimated present value amount of approximately $1,143 and $1,087 at March 31, 2019 and December 31, 2018 , 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 this guarantee, subject to its 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 contract 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 2019 , was $136 at March 31, 2019 . Pursuant to the Separation and Distribution Agreement, Arconic was required to retain letters of credit of $54 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 2019 , was $50 at March 31, 2019 . 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.

Proposed Separation Transaction

Proposed Separation Transaction	3 Months Ended
	Mar. 31, 2019
Restructuring and Related Activities [Abstract]
Proposed Separation Transaction	Proposed Separation Transaction On February 8, 2019, Arconic announced, as part of its strategy and portfolio review, a separation of its portfolio into two independent, publicly-traded companies. One company will comprise the Engineered Products and Forgings businesses and the other company will comprise the Global Rolled Products businesses. The Company will also consider the sale of businesses that do not best fit into Engineered Products and Forgings and Global Rolled Products. The businesses of the current Transportation and Construction Solutions segment will be divided, with BCS to become part of Global Rolled Products and the Arconic Wheel and Transportation Products business to become part of Engineered Products and Forgings. Arconic is targeting to complete the separation in the second quarter of 2020. The separation transaction is subject to a number of conditions, including, but not limited to, final approval by Arconic’s Board of Directors, receipt of a favorable opinion of legal counsel with respect to the tax-free nature of the transaction for U.S. federal income tax purposes, completion of financing, and the effectiveness of a Form 10 registration statement to be filed with the U.S. Securities and Exchange Commission. Arconic may, at any time and for any reason until the proposed transaction is complete, abandon the separation plan or modify or change its terms. In the first quarter of 2019, Arconic recognized $3 pre-tax in Selling, general administrative, and other expenses on the accompanying Statement of Consolidated Operations for costs related to the proposed separation transaction.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2019
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 Note F for details of the final cash contribution the Company made to its pension plan associated with the separation of Alcoa Inc. See Note H for details of the completed ASR. On April 30, 2019, Arconic reached an agreement to sell a small manufacturing facility. The sale is expected to close in the second quarter of 2019 and the Company expects to record a restructuring-related charge of approximately $10 to $15 pre-tax. The charge primarily relates to the non-cash impairment of the net book value of the business.

Recently Adopted and Recently_2

Recently Adopted and Recently Issued Accounting Guidance (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Recently Adopted and Recently Issued Accounting Guidance	Adopted In February 2016, the Financial Accounting Standards Board (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, initially measured at the present value of the future lease payments for all operating leases with a term greater than 12 months. These changes became effective for Arconic on January 1, 2019 and have been applied using the modified retrospective approach as of the date of adoption, under which leases existing at, or entered into after, January 1, 2019 were required to be recognized and measured. Prior period amounts have not been adjusted and continue to be reflected in accordance with the Company’s historical accounting. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company to carry forward the historical lease classification. The Company also elected to separate lease components from non-lease components for all classes of assets. The adoption of this new standard resulted in the Company recording operating lease right-of-use assets and lease liabilities of approximately $320 on the Consolidated Balance Sheet as of January 1, 2019. Also, the Company reclassified cash proceeds of $119 from Other noncurrent liabilities and deferred credits, assets of $24 from Properties, plants, and equipment, net, and deferred tax assets of $22 from Other noncurrent assets to Accumulated deficit reflecting the cumulative effect of an accounting change related to the sale-leaseback of the Texarkana, Texas cast house (see Note Q ). The adoption of the standard had no impact on the Statement of Consolidated Operations or Statement of Consolidated Cash Flows. In August 2017, the FASB issued guidance that made more financial and nonfinancial hedging strategies eligible for hedge accounting. It also amended the presentation and disclosure requirements and changed 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 became effective for Arconic on January 1, 2019. For cash flow hedges, Arconic recorded a cumulative effect adjustment of $2 related to eliminating the separate measurement of ineffectiveness by decreasing Accumulated other comprehensive loss and increasing Accumulated deficit on the accompanying Consolidated Balance Sheet. The amendments to presentation and disclosure are required prospectively. Arconic has determined that under the new accounting guidance it will be able to more broadly use cash flow hedge accounting for its variable priced inventory purchases and customer sales. Issued 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 2018, the FASB issued guidance that impacts disclosures for defined benefit pension plans and other postretirement benefit plans. These changes become effective for Arconic's annual report for the year ending December 31, 2020, with early adoption permitted. Management has determined that the adoption of this guidance will not have a material impact on the Consolidated Financial Statements.
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.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2019
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 First quarter ended March 31, 2019 Sales: Third-party sales $ 1,502 $ 1,503 $ 535 $ 3,540 Intersegment sales — 55 — 55 Total sales $ 1,502 $ 1,558 $ 535 $ 3,595 Profit and loss: Segment operating profit $ 253 $ 107 $ 87 $ 447 Restructuring and other charges 14 6 9 29 Provision for depreciation and amortization 64 54 13 131 First quarter ended March 31, 2018 Sales: Third-party sales $ 1,426 $ 1,481 $ 537 $ 3,444 Intersegment sales — 57 — 57 Total sales $ 1,426 $ 1,538 $ 537 $ 3,501 Profit and loss: Segment operating profit $ 209 $ 124 $ 67 $ 400 Restructuring and other charges 1 (1 ) — — Provision for depreciation and amortization 65 56 13 134
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 : First quarter ended March 31, 2019 2018 Total segment operating profit $ 447 $ 400 Unallocated amounts: Restructuring and other charges (12 ) (7 ) Corporate expense (61 ) (60 ) Consolidated operating income $ 374 $ 333 Interest expense (85 ) (114 ) Other expense, net (32 ) (20 ) Consolidated income before income taxes $ 257 $ 199
Reconciliation of Assets from Segment to Consolidated	The following table reconciles Total segment assets to Consolidated assets : March 31, 2019 December 31, 2018 Total segment assets $ 16,127 $ 15,372 Unallocated amounts: Cash and cash equivalents 1,319 2,277 Deferred income taxes 480 573 Corporate fixed assets, net 308 305 Fair value of derivative contracts 8 37 Other 119 129 Consolidated assets $ 18,361 $ 18,693 The total assets of Arconic's reportable segment were as follows: March 31, 2019 December 31, 2018 Engineered Products and Solutions $ 10,153 $ 9,797 Global Rolled Products 4,768 4,486 Transportation and Construction Solutions 1,206 1,089 Total segment assets $ 16,127 $ 15,372
Disaggregation of Revenue by Major End Market Served	The following table disaggregates revenue by major end market served. Differences between segment totals and consolidated Arconic are in Corporate: Engineered Products and Solutions Global Rolled Products Transportation and Construction Solutions Total Segment First quarter ended March 31, 2019 Aerospace $ 1,250 $ 302 $ — $ 1,552 Transportation 87 649 255 991 Building and construction — 49 281 330 Industrial and Other 165 503 (1 ) 667 Total end-market revenue $ 1,502 $ 1,503 $ 535 $ 3,540 First quarter ended March 31, 2018 Aerospace $ 1,141 $ 248 $ — $ 1,389 Transportation 73 622 243 938 Building and construction — 48 285 333 Industrial and Other 212 563 9 784 Total end-market revenue $ 1,426 $ 1,481 $ 537 $ 3,444

Restructuring and Other Charg_2

Restructuring and Other Charges (Tables)	3 Months Ended
	Mar. 31, 2019
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, 2017 $ 56 $ 2 $ 58 Cash payments (47 ) (2 ) (49 ) Restructuring charges 111 13 124 Other (1) (110 ) 2 (108 ) Reserve balances at December 31, 2018 10 15 25 Cash payments (14 ) (3 ) (17 ) Restructuring charges 11 — 11 Other (1) 57 (9 ) 48 Reserve balances at March 31, 2019 $ 64 $ 3 $ 67 (1) Other includes adjustments of previously recorded restructuring charges and credits, and the effects of foreign currency translation. In 2019, Other for layoff costs included reclassifications of a $58 credit for elimination of life insurance benefits for U.S. salaried and non-bargaining hourly retirees and a $2 pension settlement charge, as the impacts were reflected in Arconic's separate liabilities for Accrued pension benefits and Accrued postretirement benefits. Other for other exit costs included a reclassification of $9 in lease exit costs to right-of-use assets within Other noncurrent assets in accordance with the new lease accounting standard. In 2018, Other for layoff costs included reclassifications of $119 in pension costs and a $28 credit in postretirement benefits, as the impacts were reflected in Arconic's separate liabilities for Accrued pension benefits and Accrued postretirement benefits, and reversals of previously recorded restructuring charges of $19 .

Other Expense, Net (Tables)

Other Expense, Net (Tables)	3 Months Ended
	Mar. 31, 2019
Other Income and Expenses [Abstract]
Schedule of Other Nonoperating Income (Expense)	First quarter ended March 31, 2019 2018 Non-service related net periodic benefit cost $ 29 $ 28 Interest income (10 ) (6 ) Foreign currency gains, net — (3 ) Net loss from asset sales 2 3 Other, net 11 (2 ) $ 32 $ 20

Pension and Other Postretirem_2

Pension and Other Postretirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost	The components of net periodic benefit cost were as follows: First quarter ended March 31, 2019 2018 Pension benefits Service cost $ 7 $ 20 Interest cost 59 55 Expected return on plan assets (72 ) (77 ) Recognized net actuarial loss 35 42 Amortization of prior service cost (benefit) — 1 Settlements 2 — Curtailments — 5 Net periodic benefit cost (1) $ 31 $ 46 Other postretirement benefits Service cost $ 2 $ 2 Interest cost 7 7 Recognized net actuarial loss 1 2 Amortization of prior service cost (benefit) (1 ) (2 ) Curtailments (58 ) — Net periodic benefit cost (1) $ (49 ) $ 9 (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, net in the Statement of Consolidated Operations.

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Schedule of Income Tax Provisions	The tax provisions for the first quarter of 2019 and 2018 were comprised of the following: First quarter ended March 31, 2019 2018 Pre-tax income at estimated annual effective income tax rate before discrete items $ 67 $ 53 Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized 2 1 Other discrete items 1 2 Provision for income taxes $ 70 $ 56

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2019
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): First quarter ended March 31, 2019 2018 Net income $ 187 $ 143 Less: preferred stock dividends declared (1 ) (1 ) Net income available to Arconic common shareholders - basic 186 142 Add: Interest expense related to convertible notes 4 3 Net income available to Arconic common shareholders - diluted $ 190 $ 145 Average shares outstanding - basic 471 482 Effect of dilutive securities: Stock options — 5 Stock and performance awards 4 2 Convertible notes 14 14 Average shares outstanding - diluted 489 503
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). First quarter ended March 31, 2019 2018 Stock options (1) 8 6 (1) The average exercise price per share of options was $26.67 and $30.75 for the first quarter of 2019 and 2018 , respectively.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2019
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: First quarter ended March 31, 2019 2018 Pension and other postretirement benefits ( F ) Balance at beginning of period $ (2,344 ) $ (2,230 ) Other comprehensive income: Unrecognized net actuarial loss and prior service cost/benefit 72 137 Tax expense (16 ) (31 ) Total Other comprehensive income before reclassifications, net of tax 56 106 Amortization of net actuarial loss and prior service cost (1) (21 ) 48 Tax benefit (expense) (2) 5 (11 ) Total amount reclassified from Accumulated other comprehensive loss, net of tax (5) (16 ) 37 Total Other comprehensive income 40 143 Balance at end of period $ (2,304 ) $ (2,087 ) Foreign currency translation Balance at beginning of period $ (583 ) $ (437 ) Other comprehensive income (3) 26 122 Balance at end of period $ (557 ) $ (315 ) Available-for-sale securities Balance at beginning of period $ (3 ) $ (2 ) Other comprehensive income (4) 3 — Balance at end of period $ — $ (2 ) Cash flow hedges Balance at beginning of period $ 4 $ 25 Adoption of accounting standards (B) (2 ) — Other comprehensive income (loss): Net change from periodic revaluations 8 (6 ) Tax (expense) benefit (1 ) 1 Total Other comprehensive income (loss) before reclassifications, net of tax 7 (5 ) Net amount reclassified to earnings — (3 ) Tax benefit (2) — 1 Total amount reclassified from Accumulated other comprehensive income, net of tax (5) — (2 ) Total Other comprehensive income (loss) 7 (7 ) Balance at end of period $ 9 $ 18 Total balance at end of period $ (2,852 ) $ (2,386 ) (1) These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note F ). (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, 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)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2019
Inventory Disclosure [Abstract]
Schedule of Inventory Components	March 31, 2019 December 31, 2018 Finished goods $ 699 $ 668 Work-in-process 1,448 1,371 Purchased raw materials 371 366 Operating supplies 94 87 Total inventories $ 2,612 $ 2,492

Property, Plants, and Equipme_2

Property, Plants, and Equipment, Net (Tables)	3 Months Ended
	Mar. 31, 2019
Property, Plant and Equipment [Abstract]
Property, Plants, and Equipment, Net	March 31, 2019 December 31, 2018 Land and land rights $ 137 $ 136 Structures 2,357 2,364 Machinery and equipment: 9,267 9,234 11,761 11,734 Less: accumulated depreciation and amortization 6,811 6,769 4,950 4,965 Construction work-in-progress 777 739 $ 5,727 $ 5,704

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Schedule of Supplemental Balance Sheet Information Related to Leases	Operating lease right-of-use assets and lease liabilities in the Consolidated Balance Sheet were as follows: March 31, 2019 Right-of-use assets classified in Other noncurrent assets $ 302 Current portion of lease liabilities classified in Other current liabilities 94 Long-term portion of lease liabilities classified in Other noncurrent liabilities and deferred credits 215 Total lease liabilities $ 309
Schedule of Future Minimum Contractual Operating Lease Obligations	Future minimum contractual operating lease obligations were as follows: March 31, 2019 December 31, 2018 2019 $ 75 $ 94 2020 79 74 2021 59 54 2022 43 40 2023 31 30 Thereafter 91 87 Total lease payments $ 378 $ 379 Less: Imputed interest (69 ) Present value of lease liabilities $ 309

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	March 31, 2019 December 31, 2018 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) (26 ) (29 ) 6,304 6,301 Less: amount due within one year 405 405 Total long-term debt $ 5,899 $ 5,896 (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 Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of Carrying Values and Fair Values of Financial Instruments	March 31, 2019 December 31, 2018 Carrying value Fair value Carrying value Fair value Long-term debt, less amount due within one year $ 5,899 $ 6,125 $ 5,896 $ 5,873

Recently Adopted and Recently_3

Recently Adopted and Recently Issued Accounting Guidance (Details) - USD ($) $ in Millions	Jan. 01, 2019	Mar. 31, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Right-of-use assets classified in Other noncurrent assets		$ 302
Operating lease liability		$ 309
Adoption of accounting standards (B)	$ 73
Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Right-of-use assets classified in Other noncurrent assets	320
Operating lease liability	320
Accounting Standards Update 2017-12
Summary Of Significant Accounting Policies [Line Items]
Adoption of accounting standards (B)	2
Other Noncurrent Liabilities and Deferred Credits | Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Effect on retained earnings	119
Property, Plant and Equipment | Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Effect on retained earnings	(24)
Other Noncurrent Assets | Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Effect on retained earnings	$ (22)

Segment Information - Narrative

Segment Information - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Segment Reporting [Abstract]
Goodwill, amount reallocated due to restructuring	$ 110

Segment Information - Schedule

Segment Information - Schedule of Operating Results of Arconic's Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Total sales	$ 3,541	$ 3,445
Segment operating profit	447	400
Restructuring and other charges	29	0
Provision for depreciation and amortization	131	134
Operating Segments
Segment Reporting Information [Line Items]
Total sales	3,595	3,501
Intersegment sales
Segment Reporting Information [Line Items]
Total sales	55	57
Third-party sales | Operating Segments
Segment Reporting Information [Line Items]
Total sales	3,540	3,444
Engineered Products and Solutions
Segment Reporting Information [Line Items]
Segment operating profit	253	209
Restructuring and other charges	14	1
Provision for depreciation and amortization	64	65
Engineered Products and Solutions | Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,502	1,426
Engineered Products and Solutions | Intersegment sales
Segment Reporting Information [Line Items]
Total sales	0	0
Engineered Products and Solutions | Third-party sales | Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,502	1,426
Global Rolled Products
Segment Reporting Information [Line Items]
Segment operating profit	107	124
Restructuring and other charges	6	(1)
Provision for depreciation and amortization	54	56
Global Rolled Products | Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,558	1,538
Global Rolled Products | Intersegment sales
Segment Reporting Information [Line Items]
Total sales	55	57
Global Rolled Products | Third-party sales | Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,503	1,481
Transportation and Construction Solutions
Segment Reporting Information [Line Items]
Segment operating profit	87	67
Restructuring and other charges	9	0
Provision for depreciation and amortization	13	13
Transportation and Construction Solutions | Operating Segments
Segment Reporting Information [Line Items]
Total sales	535	537
Transportation and Construction Solutions | Intersegment sales
Segment Reporting Information [Line Items]
Total sales	0	0
Transportation and Construction Solutions | Third-party sales | Operating Segments
Segment Reporting Information [Line Items]
Total sales	$ 535	$ 537

Segment Information - Schedul_2

Segment Information - Schedule of Combined Segment Adjusted EBITDA to Net Income Attributable to Arconic (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Total segment operating profit	$ 447	$ 400
Restructuring and other charges	(12)	(7)
Operating income	374	333
Interest expense	(85)	(114)
Other expense, net	(32)	(20)
Consolidated income before income taxes	257	199
Segment Reconciling Items
Segment Reporting Information [Line Items]
Restructuring and other charges	(12)	(7)
Corporate expense	(61)	(60)
Operating income	374	333
Interest expense	(85)	(114)
Other expense, net	(32)	(20)
Consolidated income before income taxes	$ 257	$ 199

Segment Information - Assets By

Segment Information - Assets By Reportable Segment (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total assets	$ 18,361	$ 18,693
Operating Segments
Segment Reporting Information [Line Items]
Total assets	16,127	15,372
Engineered Products and Solutions
Segment Reporting Information [Line Items]
Total assets	10,153	9,797
Global Rolled Products
Segment Reporting Information [Line Items]
Total assets	4,768	4,486
Transportation and Construction Solutions
Segment Reporting Information [Line Items]
Total assets	$ 1,206	$ 1,089

Segment Information - Schedul_3

Segment Information - Schedule of Segment Reporting Information to Consolidated Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total assets	$ 18,361	$ 18,693
Cash and cash equivalents	1,319	2,277
Corporate fixed assets, net	5,727	5,704
Operating Segments
Segment Reporting Information [Line Items]
Total assets	16,127	15,372
Segment Reconciling Items
Segment Reporting Information [Line Items]
Cash and cash equivalents	1,319	2,277
Deferred income taxes	480	573
Corporate fixed assets, net	308	305
Fair value of derivative contracts	8	37
Other	$ 119	$ 129

Segment Information - Disaggreg

Segment Information - Disaggregation of Revenue by Major End Market Served (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue, Major Customer [Line Items]
Revenues	$ 3,540	$ 3,444
Engineered Products and Solutions
Revenue, Major Customer [Line Items]
Revenues	1,502	1,426
Global Rolled Products
Revenue, Major Customer [Line Items]
Revenues	1,503	1,481
Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Revenues	535	537
Aerospace
Revenue, Major Customer [Line Items]
Revenues	1,552	1,389
Aerospace | Engineered Products and Solutions
Revenue, Major Customer [Line Items]
Revenues	1,250	1,141
Aerospace | Global Rolled Products
Revenue, Major Customer [Line Items]
Revenues	302	248
Aerospace | Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Revenues	0	0
Transportation
Revenue, Major Customer [Line Items]
Revenues	991	938
Transportation | Engineered Products and Solutions
Revenue, Major Customer [Line Items]
Revenues	87	73
Transportation | Global Rolled Products
Revenue, Major Customer [Line Items]
Revenues	649	622
Transportation | Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Revenues	255	243
Building and construction
Revenue, Major Customer [Line Items]
Revenues	330	333
Building and construction | Engineered Products and Solutions
Revenue, Major Customer [Line Items]
Revenues	0	0
Building and construction | Global Rolled Products
Revenue, Major Customer [Line Items]
Revenues	49	48
Building and construction | Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Revenues	281	285
Industrial and Other
Revenue, Major Customer [Line Items]
Revenues	667	784
Industrial and Other | Engineered Products and Solutions
Revenue, Major Customer [Line Items]
Revenues	165	212
Industrial and Other | Global Rolled Products
Revenue, Major Customer [Line Items]
Revenues	503	563
Industrial and Other | Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Revenues	$ (1)	$ 9

Restructuring and Other Charg_3

Restructuring and Other Charges - Narrative (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019USD ($)position	Mar. 31, 2018USD ($)position	Dec. 31, 2020USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017position
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	$ 12	$ 7
Restructuring and other charges (benefits) after tax	10	5
Cash payments for restructuring	17			$ 49
Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	65	4
Restructuring and other charges (benefits) after tax	$ 51	3
Number of employees associated with layoff costs | position	800
Executive Severance Net Of The Benefit Of Forfeited Executive Stock Compensation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	$ 2
Restructuring and other charges (benefits) after tax	1
Pension Settlement Cost
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	2
Restructuring and other charges (benefits) after tax	2
Other Miscellaneous Charges
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	1
Restructuring and other charges (benefits) after tax	1
Elimination Of Life Insurance Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	(58)
Restructuring and other charges (benefits) after tax	(45)
Pension Curtailment Charge
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		5
Restructuring and other charges after tax and noncontrolling interest		4
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		2
Restructuring and other charges after tax and noncontrolling interest		1
Other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		(4)
Restructuring and other charges (benefits) after tax		$ (3)
Cash payments for restructuring	$ 3			2
Restructuring Programs Layoffs 2019
Restructuring Cost and Reserve [Line Items]
Approximate number of employees already laid off | position	247
Number of employees associated with layoff costs | position					800
Cash payments for restructuring	$ 7
Restructuring Programs Layoffs 2018
Restructuring Cost and Reserve [Line Items]
Approximate number of employees already laid off | position	115
Number of employees associated with layoff costs | position					125
Cash payments for restructuring	$ 3
Restructuring Programs Layoffs 2017
Restructuring Cost and Reserve [Line Items]
Approximate number of employees already laid off | position	570
Number of employees associated with layoff costs | position					660
Cash payments for restructuring	$ 4
Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring	$ 14			$ 47
Corporate Segment | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	425
Corporate Segment | Restructuring Programs Layoffs 2018
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position		16
Engineered Products and Solutions | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	168
Transportation and Construction Solutions | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	121
Global Rolled Products | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	86
Scenario, Forecast | Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring			$ 3

Restructuring and Other Charg_4

Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	$ 25	$ 58	$ 58
Cash payments	(17)		(49)
Restructuring charges	11		124
Other	48		(108)
Restructuring reserve ending balance	67		25
Restructuring and other charges	(12)	(7)
Layoff costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	10	56	56
Cash payments	(14)		(47)
Restructuring charges	11		111
Other	57		(110)
Restructuring reserve ending balance	64		10
Other exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	15	2	2
Cash payments	(3)		(2)
Restructuring charges	0		13
Other	(9)		2
Restructuring reserve ending balance	3		15
Restructuring and other charges		$ 4
Elimination Of Life Insurance Benefits
Restructuring Reserve [Roll Forward]
Restructuring and other charges	58
Pension Settlement Cost
Restructuring Reserve [Roll Forward]
Restructuring and other charges	(2)
Other Exit Costs, Reclassification Of Lease Exit Costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges	$ 9
Employee Severance Cost, Reclassification Of Pension Costs
Restructuring Reserve [Roll Forward]
Other			119
Employee Severance Costs, Credit In Post-Retirement Costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges			28
Employee Severance, Reversal Of Prior Restructuring
Restructuring Reserve [Roll Forward]
Restructuring and other charges			$ 19

Other Expense, Net - Schedule (

Other Expense, Net - Schedule (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Income and Expenses [Abstract]
Non-service related net periodic benefit cost	$ 29	$ 28
Interest income	(10)	(6)
Foreign currency gains, net	0	(3)
Net loss from asset sales	2	3
Other, net	11	(2)
Total	$ 32	$ 20

Pension and Other Postretirem_3

Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 7	$ 20
Interest cost	59	55
Expected return on plan assets	(72)	(77)
Recognized net actuarial loss	35	42
Amortization of prior service cost (benefit)	0	1
Settlements	2		$ 0
Curtailments	0	5
Net periodic benefit cost	31	46
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2
Interest cost	7	7
Recognized net actuarial loss	1	2
Amortization of prior service cost (benefit)	(1)	(2)
Curtailments	(58)	0
Net periodic benefit cost	$ (49)	$ 9

Pension and Other Postretirem_4

Pension and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	Nov. 01, 2016	Apr. 30, 2019	Mar. 31, 2018	Apr. 30, 2017	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restructuring and other charges (benefits)					$ 12	$ 7
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits					40	143
Aggregate cash cash contribution to pension plan	$ 150
Cash contribution term to pension plan	30 months
Cash payments made for pension and other post-retirement benefits			$ 66	$ 50
Other postretirement benefits
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Curtailment benefit (charges)					58	0
Pension Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Curtailment benefit (charges)					0	(5)
UNITED STATES | Other postretirement benefits
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Decrease in obligation, pension benefits					(63)
Curtailment benefit (charges)					(58)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits					(5)
UNITED STATES | Pension Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Decrease in obligation, pension benefits						(136)
Curtailment benefit (charges)						5
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits						$ 141
Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash payments made for pension and other post-retirement benefits		$ 34
Pension Settlement Cost
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restructuring and other charges (benefits)					2
Elimination Of Health Care Subsidies | UNITED STATES | Other postretirement benefits
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Decrease in obligation, pension benefits					$ (12)

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, percent	25.90%	26.50%
Effective income tax rate reconciliation, including discrete items, percent	27.20%	28.10%
Discrete income tax expense	$ 1	$ 2

Income Taxes - Summary of Tax P

Income Taxes - Summary of Tax Provisions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Pretax income at estimated annual effective income tax rate before discrete items	$ 67	$ 53
Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized	2	1
Other discrete items	1	2
Provision for income taxes	$ 70	$ 56

Common Stock (Details)

Common Stock (Details) - USD ($)	Apr. 29, 2019	Feb. 21, 2019	Apr. 29, 2019	Apr. 26, 2019	Mar. 31, 2019	Feb. 19, 2019	Mar. 31, 2018
Accelerated Share Repurchases [Line Items]
Common stock outstanding (in shares)					453,000,000		483,000,000
Accelerated Share Repurchase Program
Accelerated Share Repurchases [Line Items]
Accelerated stock repurchase program, shares to be repurchased, dollar amount						$ 700,000,000
Shares acquired		31,908,831
Subsequent Event
Accelerated Share Repurchases [Line Items]
Common stock outstanding (in shares)	448,629,078		448,629,078
Subsequent Event | Accelerated Share Repurchase Program
Accelerated Share Repurchases [Line Items]
Shares acquired	4,525,592		36,434,423
Purchase price of shares repurchased under ASR agreement (in dollars per share)			$ 19.21
Stock repurchase program, shares authorized				$ 300,000,000

Earnings Per Share - Reconcilia

Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 187	$ 143
Less: preferred stock dividends declared	(1)	(1)
Net income available to Arconic common shareholders - basic	186	142
Add: Interest expense related to convertible notes	4	3
Net income available to Arconic common shareholders - diluted	$ 190	$ 145
Average shares outstanding - basic (in shares)	471	482
Effect of dilutive securities:
Stock options (in shares)	0	5
Stock and performance awards (in shares)	4	2
Convertible notes (in shares)	14	14
Weighted average shares outstanding - diluted (in shares)	489	503
Common stock outstanding	453	483
Incremental common shares attributable to dilutive effect of accelerated share repurchase agreements	32

Earnings Per Share - Schedule o

Earnings Per Share - Schedule of Anti Dilutive Securities Excluded From Computation of Weighted Average Shares Outstanding (Details) - Stock options - $ / shares shares in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	8	6
Weighted average exercise price of options (in usd per share)	$ 26.67	$ 30.75

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Jan. 01, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 5,585	$ 4,924
Other comprehensive income:
Total Other comprehensive income, net of tax	76	258
Adoption of accounting standards (B)			$ 73
Balance at end of period	5,178	5,282
Arconic
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,926)	(2,644)
Other comprehensive income:
Total Other comprehensive income, net of tax	76	258
Adoption of accounting standards (B)			(2)
Balance at end of period	(2,852)	(2,386)
Pension and other postretirement benefits (F)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,344)	(2,230)
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	72	137
Tax (expense) benefit	(16)	(31)
Total Other comprehensive income before reclassifications, net of tax	56	106
Amortization of net actuarial loss and prior service cost	(21)	48
Tax benefit (expense)	5	(11)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	(16)	37
Total Other comprehensive income, net of tax	40	143
Balance at end of period	(2,304)	(2,087)
Foreign currency translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(583)	(437)
Other comprehensive income:
Total Other comprehensive income, net of tax	26	122
Balance at end of period	(557)	(315)
Available-for-sale securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(3)	(2)
Other comprehensive income:
Total Other comprehensive income, net of tax	3	0
Balance at end of period	0	(2)
Cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	4	25
Other comprehensive income:
Unrecognized net actuarial loss and prior service cost/benefit	8	(6)
Tax (expense) benefit	(1)	1
Total Other comprehensive income before reclassifications, net of tax	7	(5)
Amortization of net actuarial loss and prior service cost	0	(3)
Tax benefit (expense)	0	1
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0	(2)
Total Other comprehensive income, net of tax	7	(7)
Balance at end of period	$ 9	$ 18
Accounting Standards Update 2017-12
Other comprehensive income:
Adoption of accounting standards (B)			2
Accounting Standards Update 2017-12 | Cash flow hedges
Other comprehensive income:
Adoption of accounting standards (B)			$ (2)	$ 0

Receivables (Details)

Receivables (Details)	Mar. 30, 2012USD ($)	Mar. 31, 2019USD ($)agreement	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)
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	160,000,000	$ 136,000,000
Deferred purchase program receivable	$ 254,000,000	430,000,000		$ 234,000,000
Net cash funding received during the period		300,000,000
Amount of cash draws under arrangement during the period		3,108,000,000
Amount of cash repayments under arrangement during the period		(2,808,000,000)
Amount of cash draws under arrangement since inception		150,000,000
Amount of cash repayments under arrangement since inception		(150,000,000)
Gross amount of receivables sold		43,899,000,000
Cash collections of other receivables		43,190,000,000
Maximum
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold		$ 400,000,000

Inventories - Schedule of Inven

Inventories - Schedule of Inventory Components (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Finished goods	$ 699	$ 668
Work-in-process	1,448	1,371
Purchased raw materials	371	366
Operating supplies	94	87
Total inventories	$ 2,612	$ 2,492

Inventories - Narrative (Detail

Inventories - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventories valued on a LIFO basis	$ 1,340	$ 1,292
Total inventories valued on an average-cost basis	$ 527	$ 530

Property, Plants, and Equipme_3

Property, Plants, and Equipment, Net (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Less: accumulated depreciation and amortization	$ 6,811	$ 6,769
Properties, plants and equipment excluding construction work in progress	4,950	4,965
Construction work-in-progress	777	739
Properties, plants, and equipment, net	5,727	5,704
Land and land rights
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	137	136
Structures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,357	2,364
Machinery and equipment:
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,267	9,234
Depreciable property, plant and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 11,761	$ 11,734

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Leases [Abstract]
Operating lease expense	$ 37	$ 38
Right-of-use assets obtained in exchange for operating lease obligations	$ 6
Weighted-average remaining lease term (years)	6 years
Weighted-average discount rate	6.20%

Leases - Operating Lease Expen

Leases - Operating Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Leases [Abstract]
Operating lease expense	$ 37	$ 38

Leases - Operating Lease Assets

Leases - Operating Lease Assets and Liabilities in the Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Right-of-use assets classified in Other noncurrent assets	$ 302
Current portion of lease liabilities classified in Other current liabilities	94
Long-term portion of lease liabilities classified in Other noncurrent liabilities and deferred credits	215
Total lease liabilities	$ 309

Leases - Future Minimum Contrac

Leases - Future Minimum Contractual Operating Lease Obligations (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
2019	$ 75	$ 94
2020	79	74
2021	59	54
2022	43	40
2023	31	30
Thereafter	91	87
Lessee, Operating Lease, Liability, Payments, Due	378	379
Less: Imputed interest	(69)
Present value of lease liabilities	$ 309

Leases - Other Information Rela

Leases - Other Information Related to Operating Leases (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Right-of-use assets obtained in exchange for operating lease obligations	$ 6
Weighted-average remaining lease term (years)	6 years
Weighted-average discount rate	6.20%

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt	$ 6,304	$ 6,301
Less: amount due within one year	405	405
Long-term debt, excluding amount due within one year	5,899	5,896
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
Other
Debt Instrument [Line Items]
Other	$ (26)	$ (29)

Debt - Credit Facilities (Detai

Debt - Credit Facilities (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 715,000,000
Additions to debt (original maturities greater than three months)	150,000,000	$ 150,000,000
Parent Company
Debt Instrument [Line Items]
Additions to debt (original maturities greater than three months)	150,000,000
Repayments of borrowings	$ (150,000,000)
Weighted average interest rate outstanding borrowings, percentage	3.90%
Debt weighted average maturity term	14 days
Revolving Credit Agreement
Debt Instrument [Line Items]
Long-term line of credit	$ 3,000,000,000
Outstanding amount	0		$ 0
Additions to debt (original maturities greater than three months)			$ 0
Line of credit, amount outstanding	0
Expected Maturity Date Year 2019
Debt Instrument [Line Items]
Outstanding amount	465,000,000
Expected Maturity Date Year 2020
Debt Instrument [Line Items]
Outstanding amount	$ 250,000,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Restricted cash	$ 7	$ 6
Carrying value
Derivative [Line Items]
Long-term debt, less amount due within one year	5,899	5,896
Fair value
Derivative [Line Items]
Long-term debt, less amount due within one year	$ 6,125	$ 5,873

Acquisitions and Divestitures (

Acquisitions and Divestitures (Details) $ in Millions	Jan. 01, 2019USD ($)	Oct. 31, 2018USD ($)	Apr. 02, 2018USD ($)employee	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Restructuring and other charges (D)				$ 12	$ 7
Latin America Extrusions (LAE)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal group, consideration			$ 2
Purchase price allocation, subsequent years, remaining adjustments							$ 2
Number of employees | employee			612
Latin America Extrusions (LAE) | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal group, including discontinued operation, revenue							25
Latin America Extrusions (LAE) | Disposed of by Sale | Divested Businesses
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Restructuring and other charges (D)						$ 41
Texarkana, Texas Rolling Mill And Cast House
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Period of operationalizing rolling mill equipment of transaction closing date		36 months
Minimum required terms of leases on cast house building and equipment		18 months
Period of supply with aluminum		24 months
Gain (loss) on sale of business		$ 154
Contingent consideration				$ 45			5
Deferred gain on sale of property							$ 95
Texarkana, Texas Rolling Mill And Cast House | Ta Chen International, Inc.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Period of services performed, processing of metal		6 months
Texarkana, Texas Rolling Mill And Cast House | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net book value of disposal		$ 63
Cash received on sale of operations		302
Disposal group, consideration consideration		$ 50
Accounting Standards Update 2016-02 | Property, Plant and Equipment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Effect on retained earnings	$ (24)
Accounting Standards Update 2016-02 | Other Noncurrent Liabilities and Deferred Credits
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Effect on retained earnings	119
Accounting Standards Update 2016-02 | Other Noncurrent Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Effect on retained earnings	$ (22)

Contingencies and Commitments (

Contingencies and Commitments (Details) € in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019USD ($)	Mar. 31, 2019EUR (€)	Dec. 31, 2018USD ($)location	Mar. 31, 2019EUR (€)	Nov. 01, 2016USD ($)
Loss Contingencies [Line Items]
Number of cleanup locations | location			100
Remediation reserve balance	$ 261		$ 266
Remediation reserve balance, classified as a current liability	79		81
Payments related to remediation expenses applied against the reserve	3
Income tax examination assessment outstanding	171			€ 152
Guarantees of third party related to project financing	29
Total amount committed under outstanding surety bonds	50
Bank Loan Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount	136
Separation Agreement
Loss Contingencies [Line Items]
Total amount committed under outstanding surety bonds	25
Other Noncurrent Liabilities and Deferred Credits
Loss Contingencies [Line Items]
Combined fair value of guarantees	7		6
Other Noncurrent Liabilities and Deferred Credits | Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	1,143		1,087
Massena West, NY
Loss Contingencies [Line Items]
Remediation reserve balance	195		$ 198
Spain
Loss Contingencies [Line Items]
Established tax reserve	59	€ 52
Tax indemnification receivable	$ 28			€ 25
Alcoa Corporation
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%	1.00%
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding					$ 54

Proposed Separation Transacti_2

Proposed Separation Transaction - Narrative (Details) $ in Millions	Feb. 08, 2019company	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)
Restructuring Cost and Reserve [Line Items]
Number of independent, publicly-traded companies resulting from proposed separation transaction | company	2
Restructuring and other charges (D)		$ 12	$ 7
Business separation | Proposed Separation Transaction | Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (D)		$ 3

Subsequent Events Narrative (De

Subsequent Events Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		$ 12	$ 7
Scenario, Forecast | Minimum
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	$ 10
Scenario, Forecast | Maximum
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	$ 15

Uncategorized Items - arnc-2019

Label	Element	Value
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 75,000,000