Arconic (ARNC) 10-Q 12 Nov 20 2020 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Nov. 05, 2020
Cover [Abstract]
Document Type	10-Q
Document Period End Date	Sep. 30, 2020
Entity Registrant Name	ARCONIC CORPORATION
Entity Central Index Key	0001790982
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		109,145,215
Document Transition Report	false
Document Quarterly Report	true
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	84-2745636
Entity Address, Address Line One	201 Isabella Street,
Entity Address, Address Line Two	Suite 400,
Entity Address, City or Town	Pittsburgh,
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15212-5872
City Area Code	412)
Local Phone Number	992-2500
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	ARNC
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity File Number	1-39162

Statement of Combined Operation

Statement of Combined Operations - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Total Sales	$ 1,415	$ 1,805	$ 4,213	$ 5,569
Cost of goods sold (exclusive of expenses below) (K)	1,218	1,565	3,614	4,849
Selling, general administrative, and other expenses	59	82	194	255
Research and development expenses	8	9	27	34
Provision for depreciation and amortization	63	63	191	190
Restructuring and other charges (E)	3	64	61	104
Operating income	64	22	126	137
Interest expense	22	29	97	86
Other expenses (income), net (F)	27	0	69	(4)
Income (Loss) before income taxes	15	(7)	(40)	55
Provision for income taxes (H)	10	17	5	46
Net income (loss)	5	(24)	(45)	9
Less: Net income attributable to noncontrolling interest	0	0	0	0
Net income (loss) attributable to Arconic Corporation	$ 5	$ (24)	$ (45)	$ 9
Earnings per Share Attributable to Arconic Corporation Common Shareholders (I):
Basic (in dollars per share)	$ 0.05	$ (0.22)	$ (0.41)	$ 0.08
Diluted (in dollars per share)	$ 0.05	$ (0.22)	$ (0.41)	$ 0.08
Sales to unrelated parties
Total Sales	$ 1,391	$ 1,764	$ 4,132	$ 5,427
Sales to related parties
Total Sales	$ 24	$ 41	$ 81	$ 142

Statement of Combined Comprehen

Statement of Combined Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net income (loss)	$ 5	$ (24)	$ (45)	$ 9
Other comprehensive income, net of tax (J):
Change in unrecognized net actuarial loss and prior service benefit related to pension and other postretirement benefits	31	1	92	1
Foreign currency translation adjustments	37	45	42	59
Net change in unrecognized losses on cash flow hedges	12	0	5	0
Total Other comprehensive income, net of tax	80	46	139	60
Comprehensive income	85	22	94	69
Arconic Corporation
Net income (loss)	5	(24)	(45)	9
Other comprehensive income, net of tax (J):
Change in unrecognized net actuarial loss and prior service benefit related to pension and other postretirement benefits	31	1	92	1
Foreign currency translation adjustments	37	45	42	59
Net change in unrecognized losses on cash flow hedges	12	0	5	0
Total Other comprehensive income, net of tax	80	46	139	60
Comprehensive income	85	22	94	69
Noncontrolling interest
Net income (loss)	0	0	0	0
Other comprehensive income, net of tax (J):
Change in unrecognized net actuarial loss and prior service benefit related to pension and other postretirement benefits	0	0	0	0
Foreign currency translation adjustments	0	0	0	0
Net change in unrecognized losses on cash flow hedges	0	0	0	0
Total Other comprehensive income, net of tax	0	0	0	0
Comprehensive income	$ 0	$ 0	$ 0	$ 0

Combined Balance Sheet

Combined Balance Sheet - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 802	$ 72
Receivables from customers, less allowances of $1 in 2020 and $2 in 2019 (A)	629	384
Other receivables	129	136
Inventories (K)	901	1,137
Prepaid expenses and other current assets	60	28
Total current assets	2,521	1,757
Properties, plants, and equipment	7,336	7,210
Less: accumulated depreciation and amortization	4,628	4,466
Properties, plants, and equipment, net	2,708	2,744
Goodwill	381	386
Operating lease right-of-use assets (L)	140	125
Deferred income taxes	296	14
Other noncurrent assets	100	32
Total assets	6,146	5,058
Current liabilities:
Accounts payable, trade	836	1,061
Accrued compensation and retirement costs	132	80
Taxes, including income taxes	32	21
Environmental remediation (O)	97	83
Operating lease liabilities (L)	34	33
Other current liabilities	95	63
Total current liabilities	1,226	1,341
Long-term debt (M)	1,277	250
Accrued pension benefits (G)	1,355	63
Accrued other postretirement benefits (G)	471	1
Environmental remediation (O)	84	125
Operating lease liabilities (L)	109	96
Deferred income taxes	12	159
Other noncurrent liabilities and deferred credits	124	50
Total liabilities	4,658	2,085
Contingencies and commitments (O)
Equity
Parent Company net investment (A)	0	2,664
Common stock	1	0
Additional capital	3,332	0
Accumulated deficit	(91)	0
Accumulated other comprehensive (loss) income (J)	(1,768)	295
Total Arconic Corporation shareholders’ equity	1,474	2,959
Noncontrolling interest	14	14
Total equity	1,488	2,973
Total liabilities and equity	6,146	5,058
Accounts receivable, allowances	$ 1	$ 2

Combined Balance Sheet (Parenth

Combined Balance Sheet (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Accounts receivable, allowances	$ 1	$ 2

Statement of Combined Cash Flow

Statement of Combined Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating Activities
Net income (loss)	$ (45)	$ 9
Adjustments to reconcile net (loss) income to cash provided from operations:
Depreciation and amortization	191	190
Deferred income taxes	28	11
Restructuring and other charges (E)	61	104
Net periodic pension benefit cost (G)	61	4
Stock-based compensation	18	28
Amortization of debt issuance costs (M)	23	0
Other	(2)
Other		(7)
Changes in assets and liabilities, excluding effects of acquisitions, divestitures, and foreign currency translation adjustments:
(Increase) in receivables	(250)	(48)
Decrease (Increase) in inventories	197	(30)
(Increase) in prepaid expenses and other current assets	(24)	(12)
(Decrease) in accounts payable, trade (A)	(165)	(96)
(Decrease) in accrued expenses	(153)	(48)
Increase in taxes, including income taxes	75	13
Pension contributions	(44)	(2)
Decrease (Increase) in noncurrent assets	28	(6)
Increase in noncurrent liabilities	19	21
Cash provided from operations	18	(145)
Financing Activities
Net transfers from (to) former parent company	(216)	(69)
Separation payment to former parent company (A)	(728)
Additions to debt (original maturities greater than three months) (M)	2,400	0
Debt issuance costs (M)	(57)	0
Other	(4)	1
Payments on debt (original maturities greater than three months) (M)	(1,100)	0
Cash provided from (used for) financing activities	735	(68)
Investing Activities
Capital expenditures (A)	(126)	(120)
Proceeds from the sale of assets and businesses (N)	102	11
Cash used for investing activities	(24)	(109)
Effect of exchange rate changes on cash and cash equivalents and restricted cash	1	(2)
Net change in cash and cash equivalents and restricted cash	730	(34)
Cash and cash equivalents and restricted cash at beginning of year	72	81
Cash and cash equivalents and restricted cash at end of period	$ 802	$ 47

Statement of Changes in Combine

Statement of Changes in Combined Equity - USD ($) shares in Thousands, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Parent Company net investment	Parent Company net investmentCumulative Effect, Period of Adoption, Adjustment	Common stock	Additional capital	Accumulated deficit	Accumulated other comprehensive income (loss)	Noncontrolling interest
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 2,969		$ 2,707					$ 250	$ 12
Net income (loss)	9		9						0
Other comprehensive income (J)	60							60	0
Stockholders' Equity, Other	3		1						2
Change in ParentCo contribution	(111)		(111)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,117		2,841					264	12
Net income (loss)	(24)		(24)						0
Other comprehensive income (J)	46							46	0
Stockholders' Equity, Other	2								2
Change in ParentCo contribution	(138)		(138)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	3,003		2,679					310	14
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,973	$ 73	2,664	$ 73				295	14
Net income (loss)	(45)		46				$ (91)		0
Other comprehensive income (J)	139							139	0
Separation payment to former parent company (A)	(728)		(728)
Separation-related adjustments (A)	(324)		(2,548)			$ (3,322)		(450)
Issuance of common stock					(1,000)	(1,000)
Stock-based compensation	11					$ 11
Change in ParentCo contribution	217		217
Stockholders' Equity, Establishment of Defined Benefit Plans	(1,403)		349					(1,752)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,389		0		$ 1	3,318	(96)	(1,848)	14
Net income (loss)	5		0				5		0
Other comprehensive income (J)	80							80	0
Separation-related adjustments (A)	(8)					(8)
Stock-based compensation	6					6
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,488		$ 0		$ 1	$ 3,332	$ (91)	$ (1,768)	$ 14

The Separation and Basis of Pre

The Separation and Basis of Presentation	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Separation and Basis of Presentation	The Separation and Basis of Presentation​ The interim Consolidated Financial Statements of Arconic Corporation and its subsidiaries (“Arconic Corporation” 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 2019 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 the Company’s Annual Report on Form 10-K for the year ended December 31, 2019, which includes all disclosures required by GAAP. References in these Notes to (i) “ParentCo” refer to Arconic Inc., a Delaware corporation, and its consolidated subsidiaries (through March 31, 2020, at which time it was renamed Howmet Aerospace Inc.), and (ii) “2016 Separation Transaction” refer to the November 1, 2016 separation of Alcoa Inc., a Pennsylvania corporation, into two standalone, publicly-traded companies, Arconic Inc. and Alcoa Corporation. Change in Inventory Accounting Principle. Effective July 1, 2020, the Company changed its inventory cost method to average cost for all U.S. inventories previously carried at last-in, first-out (LIFO) cost. The effects of the change in accounting principle have been retrospectively applied to all prior periods presented in the accompanying Consolidated Financial Statements. See Note K for additional information. Statement of Consolidated Cash Flows. In preparing the Statement of Consolidated Cash Flows for the nine months ended September 30, 2020, management identified a misclassification related to the non-cash portion of properties, plants, and equipment additions. This non-cash portion is the result of the timing difference that exists between when the Company records such additions as assets on its Consolidated Balance Sheet and when such additions have been paid in cash. Accordingly, the amount of (Decrease) in accounts payable, trade previously reported in Cash used for operations for each of the three months ended March 31, 2020 and the six months ended June 30, 2020 was overstated by $35 and $43, respectively, and the amount of Capital expenditures previously reported in Cash provided from investing activities for each of the three months ended March 31, 2020 and the six months ended June 30, 2020 was understated by $35 and $43, respectively. The amounts for (Decrease) in accounts payable, trade and Capital expenditures on the accompanying Statement of Consolidated Cash Flows for the nine months ended September 30, 2020 are correctly stated. Additionally, financial information for the referenced prior periods not presented herein will be corrected, as applicable, in future filings. Coronavirus. Our operations and financial results have been, and are expected to continue to be, adversely affected by the current coronavirus (COVID-19) pandemic. Since Arconic’s launch as a standalone company on April 1, 2020, market conditions have been changing rapidly and unpredictably. As a result of the COVID-19 pandemic, several of our automotive and aerospace customers temporarily suspended operations. While many of our customers have resumed operations, the Company is unable to estimate with certainty at this time the status, frequency, or duration of any potential reoccurrences of customer shutdowns, or the duration or extent of resumed operations. In 2019, Arconic derived approximately 35% of its revenue from the ground transportation end market—including approximately 13% of its revenue from Ford, our largest customer—and 18% from the aerospace end market. Due to the impacts of COVID-19 on our customers, we are experiencing, and expect to continue experiencing, lower demand and volume for our products. These trends may lead to charges, impairments and other adverse financial impacts over time. The duration of the current disruptions to our customers and related financial impact to us has been estimated, but remains highly uncertain at this time. The impact on our business, results of operations, financial condition, liquidity, and/or cash flows will be magnified if the disruption from COVID-19 continues for an extended period. As a result of these developments, Arconic Corporation implemented several measures to mitigate the impacts of COVID-19 on the Company’s business, results of operations, financial condition, liquidity, and cash flows: • deferred initiating a dividend on common stock; • reduced the CEO’s salary and the Board of Directors’ cash compensation by 30% (see below); • reduced salaries for senior-level management by 20% and for all other salaried employees by 10% (see below); • restructuring of the salaried workforce, targeting a 10% reduction; • idling of various production facilities based on market conditions within the regions where the Company operates; • decreasing production and operating with a reduced labor force through shortened work weeks, shift reductions, layoffs, and the elimination of temporary workers and contractors at U.S.-based rolling and extrusion facilities; • implementing a combination of modified schedules, adjusted work hours, lower costs, and/or delayed raises at all rolling mill facilities in Europe, China and Russia; • suspended the 401K match program for U.S. salaried employees (see below); and • reducing capital expenditures by approximately $50, or approximately 30%. Effective September 1, 2020, the Company restored both the salaries of all salaried employees and the 401K match of all salaried U.S. employees, including executive officers, to the levels in effect prior to the actions described above. Also effective September 1, 2020, the Company restored the annual cash retainers payable to the non-employee members of the Company’s Board of Directors to the levels in effect prior to the previous reduction described above. The Separation. On February 8, 2019, ParentCo announced that its Board of Directors approved a plan to separate into two standalone, publicly-traded companies (the “Separation”). The spin-off company, Arconic Corporation, was to include the rolled aluminum products, aluminum extrusions, and architectural products operations of ParentCo, as well as the Latin America extrusions operations sold in April 2018, (collectively, the “Arconic Corporation Businesses”). The existing publicly traded company, ParentCo, was to continue to own the engine products, engineered structures, fastening systems, and forged wheels operations (collectively, the “Howmet Aerospace Businesses”). The Separation was subject to a number of conditions, including, but not limited to: final approval by ParentCo’s Board of Directors (see below); receipt of an opinion of legal counsel (received on March 31, 2020) regarding the qualification of the distribution, together with certain related transactions, as a “reorganization” within the meaning of Sections 335 and 368(a)(1)(D) of the U.S. Internal Revenue Code (i.e., a transaction that is generally tax-free for U.S. federal income tax purposes); and the U.S. Securities and Exchange Commission (the “SEC”) declaring effective a Registration Statement on Form 10, as amended, filed with the SEC on February 13, 2020 (effectiveness was declared by the SEC on February 13, 2020). On February 5, 2020, ParentCo’s Board of Directors approved the completion of the Separation by means of a pro rata distribution by ParentCo of all of the outstanding shares of common stock of Arconic Corporation to ParentCo common shareholders of record as of the close of business on March 19, 2020 (the “Record Date”). At the time of the Separation, ParentCo common shareholders were to receive one share of Arconic Corporation common stock for every four shares of ParentCo common stock (the “Separation Ratio”) held as of the Record Date (ParentCo common shareholders were to receive cash in lieu of fractional shares). In connection with the Separation, as of March 31, 2020, Arconic Corporation and Howmet Aerospace entered into several agreements to implement the legal and structural separation between the two companies; govern the relationship between Arconic Corporation and Howmet Aerospace after the completion of the Separation; and allocate between Arconic Corporation and Howmet Aerospace various assets, liabilities, and obligations, including, among other things, employee benefits, environmental liabilities, intellectual property, and tax-related assets and liabilities. These agreements included a Separation and Distribution Agreement, Tax Matters Agreement, Employee Matters Agreement, and certain Patent, Know-How, Trade Secret License and Trademark License Agreements. The Separation and Distribution Agreement identified the assets to be transferred, the liabilities to be assumed, and the contracts to be transferred to each of Arconic Corporation and Howmet Aerospace as part of the Separation, and provided for when and how these transfers and assumptions were to occur. On April 1, 2020 (the “Separation Date”), the Separation was completed and became effective at 12:01 a.m. Eastern Daylight Time. To effect the Separation, ParentCo undertook a series of transactions to separate the net assets and certain legal entities of ParentCo, resulting in a cash payment of $728 to ParentCo by Arconic Corporation from a portion of the aggregate net proceeds of previously executed financing arrangements (see Note M). In connection with the Separation, 109,021,376 shares of Arconic Corporation common stock were distributed to ParentCo stockholders. This was determined by applying the Separation Ratio to the 436,085,504 shares of ParentCo’s outstanding common stock as of the Record Date. “Regular-way” trading of Arconic Corporation’s common stock began with the opening of the New York Stock Exchange on April 1, 2020 under the ticker symbol “ARNC.” Arconic Corporation’s common stock has a par value of $0.01 per share. ParentCo incurred costs to evaluate, plan, and execute the Separation, and Arconic Corporation was allocated a pro rata portion of these costs based on segment revenue (see Cost Allocations below). ParentCo recognized $38 in the 2020 nine-month period and $25 and $44 in the 2019 third quarter and nine-month period, respectively, for such costs, of which $18 in the 2020 nine-month period and $13 and $23 in the 2019 third quarter and nine-month period, respectively, was allocated to Arconic Corporation. The allocated amounts were included in Selling, general administrative, and other expenses on the accompanying Statement of Consolidated Operations. Basis of Presentation. The Consolidated Financial Statements of Arconic Corporation are prepared in conformity with GAAP. In accordance with GAAP, certain situations require management to make estimates based on judgments and assumptions, which may affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements. These estimates are based on historical experience and, in some cases, assumptions based on current and future market experience, including considerations related to COVID-19. Management has made its best estimates using all relevant information available at the time, but it is possible that these estimates will differ from actual results and affect the Consolidated Financial Statements in future periods and potentially require adverse adjustments to the recoverability of goodwill and long-lived assets, the realizability of deferred tax assets and other judgments and estimations and assumptions that may be impacted by COVID-19. Principles of Consolidation. The Consolidated Financial Statements of Arconic Corporation include the accounts of Arconic Corporation and companies in which Arconic Corporation has a controlling interest. Intercompany transactions have been eliminated. Prior to the Separation Date, Arconic Corporation did not operate as a separate, standalone entity. Arconic Corporation’s operations were included in ParentCo’s financial results. Accordingly, for all periods prior to the Separation Date, the accompanying Consolidated Financial Statements were prepared from ParentCo’s historical accounting records and were presented on a standalone basis as if the Arconic Corporation Businesses had been conducted independently from ParentCo. Such Consolidated Financial Statements include the historical operations that were considered to comprise the Arconic Corporation Businesses, as well as certain assets and liabilities that were historically held at ParentCo’s corporate level but were specifically identifiable or otherwise attributable to Arconic Corporation. ParentCo’s net investment in these operations was reflected as Parent Company net investment on the accompanying Consolidated Financial Statements. All significant transactions and accounts within Arconic Corporation were eliminated. All significant intercompany transactions between ParentCo and Arconic Corporation were included within Parent Company net investment on the accompanying Consolidated Financial Statements. Cost Allocations. The description and information on cost allocations is applicable for all periods included in the Consolidated Financial Statements prior to the Separation Date. The Consolidated Financial Statements of Arconic Corporation include general corporate expenses of ParentCo that were not historically charged to the Arconic Corporation Businesses for certain support functions that were provided on a centralized basis, such as expenses related to finance, audit, legal, information technology, human resources, communications, compliance, facilities, employee benefits and compensation, and research and development activities. These general corporate expenses were included on the accompanying Statement of Consolidated Operations within Cost of goods sold, Selling, general administrative and other expenses, and Research and development expenses. These expenses were allocated to Arconic Corporation on the basis of direct usage when identifiable, with the remainder allocated based on the Arconic Corporation Businesses’ segment revenue as a percentage of ParentCo’s total segment revenue, as reported in the respective periods. All external debt not directly attributable to Arconic Corporation was excluded from the accompanying Consolidated Balance Sheet. Financing costs related to these debt obligations were allocated to Arconic Corporation based on the ratio of capital invested by ParentCo in the Arconic Corporation Businesses to the total capital invested by ParentCo in both the Arconic Corporation Businesses and the Howmet Aerospace Businesses, and were included on the accompanying Statement of Consolidated Operations within Interest expense. The following table reflects the allocations described above: Third quarter ended September 30, Nine months ended September 30, 2020 2019 ​ 2020 2019 Cost of goods sold (1) $ — $ 4 ​ $ — $ 11 Selling, general administrative, and other expenses (2) — 27 ​ 25 80 Research and development expenses — 1 ​ — 8 Provision for depreciation and amortization — 4 ​ 1 9 Restructuring and other charges (E) — 2 ​ 2 5 Interest expense — 29 ​ 28 86 Other expenses (income), net (F) — 1 ​ (5) 4 ​ _____________________ (1) For all periods presented, amount principally relates to an allocation of expenses for ParentCo’s retained pension and other postretirement benefit obligations associated with closed and sold operations. ​ (2) In the 2020 nine-month period and the 2019 third quarter and nine-month period, amount includes an allocation of $18, $13, and $23, respectively, for costs incurred by ParentCo associated with the Separation (see above). Management believes the assumptions regarding the allocation of ParentCo’s general corporate expenses and financing costs were reasonable. Nevertheless, the Consolidated Financial Statements of Arconic Corporation may not include all of the actual expenses that would have been incurred and may not reflect Arconic Corporation’s consolidated results of operations, financial position, and cash flows had it been a standalone company during the periods prior to the Separation Date. Actual costs that would have been incurred if Arconic Corporation had been a standalone company would depend on multiple factors, including organizational structure, capital structure, and strategic decisions made in various areas, including information technology and infrastructure. Transactions between Arconic Corporation and ParentCo, including sales to the Howmet Aerospace Businesses, were presented as related party transactions in these Consolidated Financial Statements and were considered to be effectively settled for cash at the time the transaction was recorded. The total net effect of the settlement of these transactions was reflected on the accompanying Statement of Consolidated Cash Flows as a financing activity and on the accompanying Consolidated Balance Sheet as Parent Company net investment. Cash management. The description and information on cash management is applicable for all periods included in the Consolidated Financial Statements prior to the Separation Date. Cash was managed centrally with certain net earnings reinvested locally and working capital requirements met from existing liquid funds. Accordingly, the cash and cash equivalents held by ParentCo at the corporate level were not attributed to Arconic Corporation for any of the periods presented prior to the Separation Date. Only cash amounts specifically attributable to Arconic Corporation were reflected in the accompanying Consolidated Balance Sheet. Transfers of cash, both to and from ParentCo’s centralized cash management system, were reflected as a component of Parent Company net investment on the accompanying Consolidated Balance Sheet and as a financing activity on the accompanying Statement of Consolidated Cash Flows. ParentCo had an arrangement with several financial institutions to sell certain customer receivables without recourse on a revolving basis. The sale of such receivables was completed through the use of a bankruptcy-remote special-purpose entity, which was a consolidated subsidiary of ParentCo. In connection with this arrangement, in all periods prior to January 1, 2020, certain of Arconic Corporation’s customer receivables were sold on a revolving basis to this bankruptcy-remote subsidiary of ParentCo; these sales were reflected as a component of Parent Company net investment on the accompanying Consolidated Balance Sheet. As of December 31, 2019, the amount of Arconic Corporation’s outstanding customer receivables sold to ParentCo’s subsidiary was $281. Effective January 2, 2020, in preparation for the Separation, ParentCo’s arrangement was amended to no longer include customer receivables associated with the Arconic Corporation Businesses, as well as to remove previously included customer receivables related to the Arconic Corporation Businesses not yet collected as of January 2, 2020. Accordingly, uncollected customer receivables of $281 related to the Arconic Corporation Businesses were removed from the program and the right to collect and receive the cash from the customer was returned to Arconic Corporation. ParentCo participated in several accounts payable settlement arrangements with certain vendors and third-party intermediaries. These arrangements provided that, at the vendor’s request, the third-party intermediary advance the amount of the scheduled payment to the vendor, less an appropriate discount, before the scheduled payment date and ParentCo make payment to the third-party intermediary on the date stipulated in accordance with the commercial terms negotiated with its vendors. In connection with these arrangements, certain of Arconic Corporation’s accounts payable were settled, at the vendor’s request, before the scheduled payment date; these settlements were reflected as a component of Parent Company net investment on the accompanying Consolidated Balance Sheet. As of December 31, 2019, the amount of Arconic Corporation’s accounts payables settled under such arrangements that had yet to be extinguished between ParentCo and third-party intermediaries was $1. Related Party Transactions. Transactions between the Arconic Corporation Businesses and the Howmet Aerospace Businesses have been presented as related party transactions on the accompanying Consolidated Financial Statements. Sales to the Howmet Aerospace Businesses from the Arconic Corporation Businesses were $24 and $81 in the 2020 third quarter and nine-month period, respectively, and $41 and $142 in the 2019 third quarter and nine-month period, respectively. As of September 30, 2020, outstanding receivables from the Howmet Aerospace Businesses were $13 and were included in Receivables from customers on the accompanying Consolidated Balance Sheet. Goodwill. During the first quarter of 2020, the equity value of Arconic Corporation’s peer group companies, and the overall U.S. stock market declined significantly amid market volatility. In addition, as a result of the COVID-19 pandemic and measures designed to contain the spread, sales globally to customers in the ground transportation and aerospace industries that are impacted by COVID-19 have been and are expected to be negatively impacted as a result of disruption in demand. As a result of these macroeconomic factors, the Company performed a qualitative assessment to evaluate whether it is more likely than not that the fair value of any of its reporting units is less than the respective carrying values. As a result of this assessment, the Company concluded that no further analysis was required and no impairment exists. The Company revisited this assessment in both the second and third quarters of 2020 amid the continued widespread impact of COVID-19 and arrived at the same conclusion. If Arconic Corporation’s actual results or external market factors further decline significantly, future goodwill impairment charges may be necessary and could be material.

Recently Adopted and Recently I

Recently Adopted and Recently Issued Accounting Guidance	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Recently Adopted and Recently Issued Accounting Guidance	Recently Adopted and Recently Issued Accounting Guidance​ Adopted On January 1, 2020, Arconic Corporation adopted changes issued by the Financial Accounting Standards Board (FASB) to credit losses. This guidance added a new impairment model (known as the current expected credit loss (CECL) model), which is based on expected losses rather than incurred losses. Under this model, an entity is required to recognize an allowance equivalent to 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. This model does not have a minimum threshold for recognition of impairment losses and requires the measurement of expected credit losses on assets that have a low risk of loss. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements. This guidance will need to be considered in future assessments of credit losses. Issued In March 2020, the FASB issued guidance that provides optional expedients and exceptions for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. These expedients and exceptions may be used when applying GAAP, if certain criteria are met, to contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of such reform. The purpose of this guidance is to provide relief to entities from experiencing unintended accounting and/or financial reporting outcomes or consequences due to reference rate reform. This guidance became effective immediately on March 12, 2020 and may be applied prospectively to contract modifications made and hedging relationships entered into or evaluated on or before December 31, 2022, after which time the expedients and exceptions expire. As of September 30, 2020, the Company has not experienced any unintended outcomes or consequences of reference rate reform that would necessitate the adoption of this guidance. Additionally, the Company will not need to consider the application of this guidance related to its credit agreement, which is scheduled to mature on May 13, 2025 and provides a credit facility that is referenced to LIBOR in certain borrowing situations (see Note M), as the terms of such agreement currently provide for a replacement rate if LIBOR is discontinued by the end of 2021 as expected. That said, management will continue to closely monitor all potential instances of reference rate reform to determine if adoption of this guidance becomes necessary in the future.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers​ The following table disaggregates revenue by major end market served. Third quarter ended September 30, Rolled Building and Extrusions Total 2020 ​ ​ ​ ​ Ground Transportation $ 493 $ — $ 25 $ 518 Building and Construction 42 241 — 283 Aerospace 107 — 44 151 Industrial Products and Other 252 — 13 265 Packaging 198 — — 198 Total end-market revenue $ 1,092 $ 241 $ 82 $ 1,415 2019 ​ ​ ​ ​ Ground Transportation $ 592 $ — $ 26 $ 618 Building and Construction 47 282 — 329 Aerospace 243 — 68 311 Industrial Products and Other 279 — 32 311 Packaging 236 — — 236 Total end-market revenue $ 1,397 $ 282 $ 126 $ 1,805 Nine months ended September 30, ​ Rolled Building and Extrusions Total 2020 ​ ​ ​ ​ ​ Ground Transportation ​ $ 1,242 $ — $ 62 $ 1,304 Building and Construction ​ 110 727 — 837 Aerospace ​ 505 — 183 688 Industrial Products and Other ​ 766 — 51 817 Packaging ​ 571 — — 571 Total end-market revenue ​ $ 3,194 $ 727 $ 296 $ 4,217 2019 ​ ​ ​ ​ Ground Transportation $ 1,878 $ — $ 88 $ 1,966 Building and Construction 149 855 — 1,004 Aerospace 754 — 221 975 Industrial Products and Other 826 — 111 937 Packaging 687 — — 687 Total end-market revenue $ 4,294 $ 855 $ 420 $ 5,569

Segment and Related Information

Segment and Related Information​	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Segment and Related Information​	Segment and Related Information​ Effective in the second quarter of 2020, management elected to change the profit or loss measure of the Company’s reportable segments from Segment operating profit to Segment Adjusted EBITDA (Earnings before interest, taxes, depreciation, and amortization) for internal reporting and performance measurement purposes. This change was made to enhance the transparency and visibility of the underlying operating performance of each segment. Effective in the third quarter of 2020, management refined the Company’s Segment Adjusted EBITDA measure to remove the impact of metal price lag (see footnote 4 to the Segment Adjusted EBITDA reconciliation below). This change was made to further enhance the transparency and visibility of the underlying operating performance of each segment by removing the volatility associated with metal prices. Arconic Corporation calculates Segment Adjusted EBITDA as Total sales (third-party and intersegment) minus each of (i) Cost of goods sold, (ii) Selling, general administrative, and other expenses, and (iii) and Research and development expenses, plus Stock-based compensation expense and Metal price lag. Previously, the Company calculated Segment operating profit as Segment Adjusted EBITDA minus each of (i) the Provision for depreciation and amortization, (ii) Stock-based compensation expense, and (iii) Metal price lag. Arconic Corporation’s Segment Adjusted EBITDA may not be comparable to similarly titled measures of other companies’ reportable segments. Also, effective July 1, 2020, the Company changed its inventory cost method to average cost for all U.S. inventories previously carried at LIFO cost. The effects of the change in accounting principle have been retrospectively applied to all prior periods presented in the accompanying Consolidated Financial Statements. See Note K for additional information. Segment information for all prior periods presented was recast to reflect the new measure of segment profit or loss and the change in inventory cost method. The operating results of the Company’s reportable segments were as follows (differences between segment totals and consolidated amounts are in Corporate): Third quarter ended September 30, ​ Rolled Building and Extrusions Total 2020 ​ ​ ​ ​ ​ Sales: ​ ​ ​ ​ ​ Third-party sales-unrelated party ​ $ 1,073 $ 241 $ 77 $ 1,391 Third-party sales-related party ​ 19 — 5 24 Intersegment sales ​ 3 — 1 4 Total sales ​ $ 1,095 $ 241 $ 83 $ 1,419 Segment Adjusted EBITDA (1) ​ $ 138 $ 40 $ (6) $ 172 Provision for depreciation and amortization ​ $ 48 $ 5 $ 6 $ 59 2019 ​ Sales: ​ Third-party sales-unrelated party ​ $ 1,366 $ 282 $ 116 $ 1,764 Third-party sales-related party ​ 31 — 10 41 Intersegment sales ​ 4 — 1 5 Total sales ​ $ 1,401 $ 282 $ 127 $ 1,810 Segment Adjusted EBITDA (1),(2) ​ $ 160 $ 39 $ (8) $ 191 Provision for depreciation and amortization ​ $ 46 $ 4 $ 7 $ 57 Nine months ended September 30, ​ Rolled Building and Extrusions Total 2020 ​ ​ ​ ​ ​ Sales: ​ ​ ​ ​ ​ Third-party sales-unrelated party ​ $ 3,144 $ 727 $ 265 $ 4,136 Third-party sales-related party ​ 50 — 31 81 Intersegment sales ​ 14 — 1 15 Total sales ​ $ 3,208 $ 727 $ 297 $ 4,232 Segment Adjusted EBITDA (1) ​ $ 388 $ 107 $ (12) $ 483 Provision for depreciation and amortization ​ $ 147 $ 14 $ 18 $ 179 2019 ​ Sales: ​ Third-party sales-unrelated party ​ $ 4,193 $ 855 $ 379 $ 5,427 Third-party sales-related party ​ 101 — 41 142 Intersegment sales ​ 20 — 1 21 Total sales ​ $ 4,314 $ 855 $ 421 $ 5,590 Segment Adjusted EBITDA (1),(2) ​ $ 499 $ 96 $ (6) $ 589 Provision for depreciation and amortization ​ $ 139 $ 14 $ 22 $ 175 The following table reconciles total Segment Adjusted EBITDA to consolidated net income (loss) attributable to Arconic Corporation: Third quarter ended September 30, Nine months ended September 30, 2020 2019 2020 2019 Total Segment Adjusted EBITDA (1),(2) $ 172 $ 191 $ 483 $ 589 Unallocated amounts: Corporate expenses (1),(3) (6) (10) (15) (43) Stock-based compensation expense (6) (10) (18) (28) Metal price lag (4) (16) (10) (30) (33) Provision for depreciation and amortization (63) (63) (191) (190) Restructuring and other charges (E) (3) (64) (61) (104) Other (1),(5) (14) (12) (42) (54) Operating income (2) 64 22 126 137 Interest expense (22) (29) (97) (86) Other (expenses) income, net (1) (F) (27) — (69) 4 Provision for income taxes (2) (10) (17) (5) (46) Net income attributable to noncontrolling interest — — — — Consolidated net income (loss) attributable to Arconic Corporation (2) $ 5 $ (24) $ (45) $ 9 ________________ ​ (1) In preparation for the Separation, effective January 1, 2020, certain U.S. defined benefit pension and other postretirement plans previously sponsored by ParentCo were separated into standalone plans for both Arconic Corporation and Howmet Aerospace. Additionally, effective April 1, 2020, Arconic Corporation assumed a portion of the obligations associated with certain non-U.S. defined benefit pension plans that included participants related to both the Arconic Corporation Businesses and the Howmet Aerospace Businesses, as well as legacy defined benefit pension plans assigned to the Company as a result of the Separation. As a result, beginning in the first quarter of 2020 for these U.S. plans and in the second quarter of 2020 for these non-U.S. plans, Arconic Corporation applied defined benefit plan accounting resulting in benefit plan expense being recorded in operating income (service cost) and nonoperating income (nonservice cost). In all historical periods prior to these respective timeframes, Arconic Corporation was considered a participating employer in ParentCo’s defined benefit plans and, therefore, applied multiemployer plan accounting resulting in the Company’s share of benefit plan expense being recorded entirely in operating income. Also, Arconic Corporation is the plan sponsor of certain other non-U.S. defined benefit plans that contain participants related only to the Arconic Corporation Businesses and, therefore, the related benefit plan expense was recorded in accordance with defined benefit plan accounting in all periods presented. The following table presents the total benefit plan expense (excluding settlements and curtailments) recorded by Arconic Corporation based on the foregoing in each period presented: Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 2020 ​ 2019 Segment Adjusted EBITDA: Rolled Products $ (5) $ (16) $ (13) $ (47) Building and Construction Systems — (1) (1) (4) Extrusions (2) (4) (5) (13) Segment total (7) (21) (19) (64) Unallocated amounts: Corporate expenses — (3) — (11) Other — (3) 1 (7) Subtotal — (6) 1 (18) Other expenses, net (20) (1) (59) (2) Total $ (27) $ (28) $ (77) $ (84) (2) Effective July 1, 2020, the Company changed its inventory cost method to average cost for all U.S. inventories previously carried at LIFO cost. The effects of the change in accounting principle have been retrospectively applied to all prior periods presented in the accompanying Consolidated Financial Statements. See Note K for additional information. (3) Corporate expenses are composed of general administrative and other expenses of operating the corporate headquarters and other global administrative facilities, as well as research and development expenses of the corporate technical center. Amounts presented for all periods prior to second quarter 2020 represent an allocation of ParentCo’s corporate expenses (see Cost Allocations in Note A). (4) Metal price lag represents the financial impact of the timing difference between when aluminum prices included in Sales are recognized and when aluminum purchase prices included in Cost of goods sold are realized. This adjustment aims to remove the effect of the volatility in metal prices and the calculation of this impact considers applicable metal hedging transactions. (5) Other includes certain items that impact Cost of goods sold and Selling, general administrative, and other expenses on the Company’s Statement of Consolidated Operations that are not included in Segment Adjusted EBITDA.

Restructuring and Other Charges

Restructuring and Other Charges	9 Months Ended
	Sep. 30, 2020
Restructuring and Related Activities [Abstract]
Restructuring and Other Charges	Restructuring and Other Charges​ In the 2020 third quarter, Arconic Corporation recorded a net charge of $3 in Restructuring and other charges, which were comprised of the following components: a $3 charge for the settlement of certain employee retirement benefits (see Note G); a $2 credit for the reversal of reserves established in prior periods; a $1 charge for layoff costs associated with the separation of approximately 30 employees in the Extrusions segment in response to the impact of COVID 19; and a $1 charge for other items. In the 2020 nine-month period, Arconic Corporation recorded a net charge of $61 in Restructuring and other charges, which were comprised of the following components: a $58 charge for the settlement of certain employee retirement benefits (see Note G); a $25 net gain related to the sales of an extrusions plant in South Korea and an aluminum rolling mill in Brazil (see Note N); an $18 charge for layoff costs associated with the separation of approximately 440 employees across the Company in response to the impact of COVID 19 (see Note A); a $14 credit for the reversal of reserves established in prior periods, including $5 related to an environmental matter (see Note O); an $11 charge for costs, of which $8 is for layoff costs associated with approximately 140 employees, related to the planned closure and related reorganizations of several small facilities in the Building and Construction Systems and Extrusions segments; a $4 charge for legacy non-income tax matters in Brazil; a $2 charge for an allocation of ParentCo’s corporate restructuring activity (see Cost Allocations in Note A); and a $7 charge for other items. In the 2019 third quarter and nine-month period, Arconic Corporation recorded a net charge of $64 and $104, respectively, in Restructuring and other charges, which were comprised of the following components: a $59 impairment charge (both periods) for the assets associated with an aluminum rolling mill in Brazil as a result of signing a definitive sale agreement (see Note N); a $3 and $28 charge, respectively, for layoff costs, including the separation of approximately 120 and 370 employees, respectively, (all within the Rolled Products and Building and Construction Systems segments); a $10 charge (nine-month period) for the impairment of the carrying value of a tradename intangible asset; a $2 and $5 net charge, respectively, for an allocation of ParentCo’s corporate restructuring activity (see Cost Allocations in Note A); and a $2 net charge (nine-month period) for other items. Arconic Corporation does not include Restructuring and other charges in the results of its reportable segments. The impact of allocating such charges to segment results would have been as follows: Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Rolled Products $ (1) $ 61 $ 15 $ 69 Building and Construction Systems — 2 6 31 Extrusions 1 (1) (27) (1) Segment total — 62 (6) 99 Corporate 3 2 67 5 $ 3 $ 64 $ 61 $ 104 As of September 30, 2020, approximately 310 of the 580 employees associated with 2020 restructuring programs and approximately 340 of the 370 (previously 480) employees associated with 2019 restructuring programs were separated. The total number of employees associated with 2019 restructuring programs was updated to reflect the reversal of a program initiated by ParentCo in 2019, natural attrition, and employees initially identified for separation accepting other positions within the Company. Most of the remaining separations for the 2020 and 2019 restructuring programs are expected to be completed during the remainder of 2020. In the 2020 third quarter and nine-month period, Arconic Corporation made cash payments of $3 and $8, respectively, against layoff reserves related to 2020 restructuring programs and $2 and $8, respectively, against layoff reserves related to 2019 restructuring programs. Activity and reserve balances for restructuring charges were as follows: ​ Layoff costs Other costs Total Reserve balances at December 31, 2018 $ 1 $ 3 $ 4 Cash payments (12) (3) (15) Restructuring charges 30 2 32 Other (1) 1 (1) — Reserve balances at December 31, 2019 20 1 21 Separation-related adjustments (2) 2 — 2 Cash payments (16) (2) (18) Restructuring charges 26 3 29 Other (1) (9) (1) (10) Reserve balances at September 30, 2020 (3) $ 23 $ 1 $ 24 _____________________ ​ (1) Other includes reversals of previously recorded restructuring charges and the effects of foreign currency translation.​ (2) Represents liabilities transferred from ParentCo on April 1, 2020 in connection with the Separation (see Note A).​ (3) The remaining reserves are expected to be paid in cash during the remainder of 2020, with the exception of $12 that is expected to be paid in 2021 ($11) and 2022 ($1) related to special termination benefits.​

Other Expenses (Income), Net

Other Expenses (Income), Net	9 Months Ended
	Sep. 30, 2020
Other Income and Expenses [Abstract]
Other Expenses (Income), Net	Other Expenses (Income), Net​ Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Non-service costs — Pension and OPEB (G) $ 20 $ 1 $ 59 $ 2 Foreign currency losses (gains), net 5 2 ​ 13 (3) Interest income — (3) ​ (4) (11) Other, net 2 — ​ 1 8 ​ $ 27 $ — ​ $ 69 $ (4)

Pension and Other Postretiremen

Pension and Other Postretirement Benefits	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits	Pension and Other Postretirement Benefits​ Arconic Corporation sponsors several defined benefit pension and other postretirement plans covering eligible employees and retirees in U.S. and foreign locations, as well as certain legacy plans previously sponsored by ParentCo. Prior to January 1, 2020 for U.S. plans and prior to April 1, 2020 for certain non-U.S. plans, eligible employees and retirees related to the Arconic Corporation Businesses participated in ParentCo-sponsored defined benefit pension and other postretirement plans (the “Shared Plans”), which included participants related to the Howmet Aerospace Businesses and ParentCo corporate participants, as well as eligible retirees from previously closed or sold operations. Also, prior to the Separation Date, other eligible employees and retirees related to the Arconic Corporation Businesses participated in certain non-U.S. defined benefit pension and other postretirement plans (the “Direct Plans”). The Company accounted for the portion of the Shared Plans related to its employees as multiemployer benefit plans. Accordingly, Arconic Corporation did not record an asset or liability to recognize the funded status of the Shared Plans. However, the related pension and other postretirement benefit expenses attributable to Arconic Corporation were based primarily on pensionable compensation of active Arconic Corporation participants and estimated interest costs, respectively. The Company also recorded an allocation of pension and other postretirement benefit expenses for the Shared Plans attributable to ParentCo corporate participants, as well as to participants related to closed and sold operations (see Cost Allocations in Note A). The Direct Plans were accounted for as defined benefit pension and other postretirement plans. Accordingly, the funded status of each Direct Plan was recorded in the Company’s Consolidated Balance Sheet. Actuarial gains and losses that had not yet been recognized in earnings were recorded in Accumulated other comprehensive loss until they were amortized as a component of net periodic benefit cost. The determination of benefit obligations and recognition of expenses related to Direct Plans were dependent on various assumptions, including discount rates, long-term expected rates of return on plan assets, and future compensation increases. Management developed each assumption using relevant company experience in conjunction with market-related data for each of the plans. In preparation for the Separation, effective January 1, 2020, certain U.S. pension and other postretirement benefit plans previously sponsored by ParentCo (the “U.S. Shared Plans” – see above) were separated into standalone plans for both Arconic Corporation (the “New Direct Plans”) and Howmet Aerospace. Accordingly, on January 1, 2020, Arconic Corporation recognized an aggregate liability of $1,920, of which $60 was current, reflecting the combined net unfunded status of the New Direct Plans, comprised of a benefit obligation of $4,255 and plan assets of $2,335, as well as $1,752 (net of tax impact) in Accumulated other comprehensive loss representing a net actuarial loss. In 2020, Arconic Corporation expects to recognize approximately $100 in combined net periodic benefit cost, of which approximately $25 is service cost. Also, in 2020, Arconic Corporation expects to make approximately $260 in pension contributions and $55 in other postretirement benefit payments, related to the New Direct Plans. Additionally, effective on the Separation Date, certain other Shared Plans (the “Additional New Direct Plans,” and, collectively with the Direct Plans and New Direct Plans, the “Cumulative Direct Plans”) were assumed by Arconic Corporation. Accordingly, on April 1, 2020, Arconic Corporation recognized a noncurrent asset of $65 and a noncurrent liability of $15, reflecting the combined net funded status of the Additional New Direct Plans, as well as $50 (net of tax impact) in Accumulated other comprehensive loss representing a net actuarial loss. In 2020, the Company expects to make approximately $280 in pension contributions to the Cumulative Direct Plans. This amount includes the previously mentioned $260 related to the New Direct Plans and $10 related to a non-U.S. plan (see below). The following table summarizes the total expenses (excluding settlements and curtailments) recognized by Arconic Corporation related to the pension and other postretirement benefits described above: ​ ​ ​ Pension benefits Other postretirement benefits ​ ​ ​ Third quarter ended September 30, Nine months ended September 30, Third quarter ended September 30, Nine months ended September 30, Type of Plan ​ Type of Expense 2020 ​ 2019 2020 ​ 2019 2020 ​ 2019 2020 ​ 2019 Cumulative Direct Plans ​ Net periodic benefit cost $ 22 $ 1 $ 61 $ 4 $ 5 $ — $ 17 $ — Shared Plans ​ Multiemployer contribution — 16 — 46 — 4 — 15 Shared Plans ​ Cost allocation — 5 (1) 15 — 2 — 4 ​ ​ ​ $ 22 $ 22 $ 60 $ 65 $ 5 $ 6 $ 17 $ 19 The components of net periodic benefit cost for defined benefit plans classified as Cumulative Direct Plans were as follows: Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Pension benefits Service cost $ 6 $ 1 $ 16 $ 2 Interest cost 27 1 81 3 Expected return on plan assets (42) (2) (127) (4) Recognized net actuarial loss 31 1 92 3 Amortization of prior service benefit — — (1) — Settlement 3 — 58 — Net periodic benefit cost* $ 25 $ 1 $ 119 $ 4 Other postretirement benefits Service cost $ 1 $ — $ 3 $ — Interest cost 2 — 10 — Recognized net actuarial loss 3 — 6 — Amortization of prior service benefit (1) — (2) — Net periodic benefit cost* $ 5 $ — $ 17 $ — ​ __________________ * Service cost was included within Cost of goods sold, Settlement was included within Restructuring and other charges, and all other components were included in Other expenses (income), net on the accompanying Statement of Consolidated Operations. U.K. Pension Plan Annuitization— In June 2020, Arconic Corporation and Howmet Aerospace, together, executed several liability management actions related to approximately 1,800 participants in a U.K. defined benefit pension plan. The primary action was the purchase of a group annuity contract to transfer the obligation to pay the remaining retirement benefits of certain plan participants to an insurance company. On a combined basis, these actions resulted in the settlement of approximately $400 in plan obligations and the transfer of approximately $460 in plan assets. In the 2020 second quarter, the Company contributed $10 to the plan to facilitate these actions and maintain the funding level of the remaining plan obligations. Prior to these actions, this plan had approximately 3,350 participants combined. Accordingly, this plan was required to be remeasured, and through this process, the discount rate was updated to 1.55% at June 30, 2020 from 2.05% at December 31, 2019. The settlement events, together with the remeasurement of the plan, resulted in a $250 net reduction to the Company’s remaining plan obligation and both a decrease to the Company’s pension benefit asset and a settlement charge of $58 in the 2020 nine-month period ($3 in the 2020 third quarter). The settlement charge represents the accelerated amortization of a portion of the existing net actuarial loss associated with this plan. This amount was reclassified to earnings through Restructuring and other charges (see Note E) from Accumulated other comprehensive loss. Subsequent to this remeasurement, the remaining respective plan obligations and plan assets attributable to Arconic Corporation and Howmet Aerospace were transferred into separate plans and the existing U.K. plan was terminated. Immediately following the completion of the transfer, the Company’s remaining plan obligation was approximately $240 and the plan assets were approximately $260 related to 1,050 plan participants. U.S. OPEB Plan Amendment— In July 2020, Arconic Corporation and the United Steelworkers agreed to modify the medical benefit coverage offered to certain Medicare-eligible participants under the Company's U.S. other postretirement benefit plan, as provided for in the current master collective bargaining agreement between the parties. Effective January 1, 2021, this modification results in lower premiums and increased benefits to the participants. This change qualifies as a significant plan amendment to the Company's U.S. other postretirement benefit plan. Accordingly, this plan was required to be remeasured, and through this process, the discount rate was updated to 2.54% at July 31, 2020 from 3.17% at December 31, 2019. The amendment, together with the remeasurement of this plan, resulted in a net decrease to both the Company's other

Income Taxes_

Income Taxes​	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes​ Arconic Corporation’s year-to-date tax provision is comprised of the most recent estimated annual effective tax rate applied to year-to-date pretax ordinary income. The tax impacts 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 pretax losses. For the 2020 nine-month period, the estimated annual effective tax rate, before discrete items, applied to ordinary loss was 11.7% (benefit on a loss). This rate differs by 9.3 percentage points from the U.S. federal statutory rate of 21.0% primarily due to nondeductible costs in the United States, U.S. tax on foreign earnings, foreign losses taxed in lower rate jurisdictions, and losses in foreign jurisdictions subject to existing valuation allowances. For the 2019 nine-month period, the estimated annual effective tax rate, before discrete items, applied to ordinary income was 80.0% (provision on income). This rate differs by 59.0 percentage points from the U.S. federal statutory rate of 21.0% primarily due to foreign income taxed in higher rate jurisdictions, losses in foreign jurisdictions subject to existing valuation allowances, certain nondeductible costs related to the Separation, estimated U.S. tax on Global Intangible Low-Taxed Income, and the state tax impact of domestic taxable income. For the third quarter of 2020 and 2019, the effective tax rate, including discrete items, was 66.7% (provision on income) and 242.9% (provision on a loss), respectively. The tax provisions for the third quarter of 2020 and 2019 were comprised of the following components: Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Pretax income at estimated annual effective income tax rate before discrete items $ 2 $ (5) ​ $ (5) $ 45 Impact of change in estimated annual effective tax rate on previous quarter’s pretax income 51 22 — — Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized* (48) — ​ 1 — Other discrete items 5 — ​ 9 1 Provision for income taxes $ 10 $ 17 ​ $ 5 $ 46 __________________ * The interim period impact related to operational losses in foreign jurisdictions for which no tax benefit is recognized will reverse by the end of the calendar year.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Basic earnings per share (EPS) amounts are computed by dividing Net income (loss) attributable to Arconic Corporation by the weighted-average number of common shares outstanding. Diluted EPS amounts assume the issuance of common stock for all potentially dilutive share equivalents outstanding. The share information used to compute basic and diluted EPS attributable to Arconic Corporation common shareholders was as follows (shares in millions): Third quarter ended September 30, Nine months ended September 30, ​ 2020 ​ 2019 2020 ​ 2019 Weighted-average shares outstanding – basic ​ 109 109 109 109 Effect of dilutive share equivalents: ​ Stock options — — — — Stock units 4 — — — Weighted-average shares outstanding – diluted 113 109 109 109 In the 2020 nine-month period, basic weighted-average shares outstanding and diluted weighted-average shares outstanding were the same because the effect of common share equivalents was anti-dilutive since Arconic Corporation generated a net loss. Had Arconic Corporation generated net income in the 2020 nine-month period, 2 million common share equivalents, respectively, related to outstanding stock units and stock options would have been included in diluted weighted-average shares outstanding. These common share equivalents do not consider 1 million stock options outstanding as of September 30, 2020 with a weighted average exercise price of $27.97 as the respective exercise price of these options was greater than the average market price of Arconic Corporation’s common stock. Prior to the Separation Date, Arconic Corporation did not have any publicly-traded issued and outstanding common stock or any common share equivalents. Accordingly, in the 2019 third quarter and nine-month period, the EPS included on the accompanying Statement of Consolidated Operations was calculated based on the 109,021,376 shares of Arconic Corporation common stock distributed on the Separation Date in connection with the completion of the Separation (see Note A).

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income​	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Accumulated Other Comprehensive Income​	Accumulated Other Comprehensive (Loss) Income​ The following table details the activity of the three components that comprise Accumulated other comprehensive (loss) income for Arconic Corporation (such activity for Noncontrolling interest was immaterial for all periods presented): Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Pension and other postretirement benefits (G) ​ ​ ​ Balance at beginning of period $ (1,784) $ (32) ​ $ (43) $ (32) Establishment of additional defined benefit plans — — (1,752) — Separation-related adjustments (A) — — (50) — Other comprehensive income: ​ Unrecognized net actuarial loss and prior service benefit 4 1 ​ (34) (1) Tax (expense) benefit (1) (1) ​ 8 — Total Other comprehensive income (loss) before reclassifications, net of tax 3 — ​ (26) (1) Amortization of net actuarial loss and prior service benefit (1) 36 1 ​ 153 3 Tax expense (2) (8) — ​ (35) (1) Total amount reclassified from Accumulated other comprehensive loss, net of tax (5) 28 1 ​ 118 2 Total Other comprehensive income 31 1 ​ 92 1 Balance at end of period $ (1,753) $ (31) ​ $ (1,753) $ (31) Foreign currency translation ​ Balance at beginning of period $ (53) $ 296 ​ $ 338 $ 282 Separation-related adjustments (A) — — (396) — Other comprehensive income: Foreign currency translation (3) 37 45 20 59 Net amount reclassified to earnings from Accumulated other comprehensive income (3),(5) — — 22 — Total Other comprehensive income 37 45 ​ 42 59 Balance at end of period $ (16) $ 341 ​ $ (16) $ 341 Cash flow hedges Balance at beginning of period $ (11) $ — $ — $ — Separation-related adjustments (A) — — (4) — Other comprehensive income: Net change from periodic revaluations 2 — 4 — Tax expense (1) — (1) — Total Other comprehensive income before reclassifications, net of tax 1 — ​ 3 — Net amount reclassified to earnings (4) 14 — 3 — Tax expense (2) (3) — (1) — Total amount reclassified from Accumulated other comprehensive loss, net of tax (5) 11 — ​ 2 — Total Other comprehensive income 12 — ​ 5 — Balance at end of period $ 1 $ — ​ $ 1 $ — Accumulated other comprehensive (loss) income $ (1,768) $ 310 ​ $ (1,768) $ 310 _____________________ (1) These amounts were included in the non-service component of net periodic benefit cost for pension and other postretirement benefits (see Note G). In the 2020 third quarter and nine-month period, these amounts include $3 and $58 related to the settlement of certain pension benefits (see Note G). (2) These amounts were reported 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. In the 2020 nine-month period, the net amount reclassified to earnings was reported in Restructuring and other charges on the accompanying Statement of Consolidated Operations related to the sale of certain foreign subsidiaries. (4) These amounts relate to aluminum contracts, a portion of which were reported in both Sales and Cost of goods sold 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. These amounts were reflected on the accompanying Statement of Consolidated Operations in the line items indicated in footnotes 1 through 4.

Inventories

Inventories	9 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Inventories	Inventories ​ September 30, 2020 ​ December 31, 2019 Finished goods $ 242 $ 237 Work-in-process 525 746 Purchased raw materials 66 85 Operating supplies 68 69 ​ $ 901 $ 1,137 Effective July 1, 2020, the Company changed its inventory cost method to average cost for all U.S. inventories previously carried at LIFO cost. Management determined that this change in accounting principle is preferable because the average cost method more closely reflects the physical flow of inventories, improves comparability of the Company’s operating results with its industry peers, and provides an increased level of consistency in the measurement of inventories in the Company’s consolidated financial statements. All non-U.S. inventories and a small portion of U.S. inventories were previously, and continue to be, measured using a combination of first in, first out (FIFO) and average cost methods. The effects of the change in accounting principle from LIFO to average cost have been retrospectively applied to all prior periods presented. This change resulted in an increase to Parent Company net investment of $293 as of January 1, 2019. Additionally, certain financial statement line items in the accompanying Consolidated Balance Sheet as of December 31, 2019 and each of the Statement of Consolidated Operations, Statement of Consolidated Comprehensive Income, and Statement of Consolidated Cash Flows for the 2019 third quarter and nine-month period were recast as follows: As Previously Reported Effect of Change As Recast Statement of Consolidated Operations for the third quarter ended September 30, 2019: Cost of goods sold $ 1,543 $ 22 $ 1,565 Operating income 44 (22) 22 Income (loss) before income taxes 15 (22) (7) Provision for income taxes 22 (5) 17 Net loss (7) (17) (24) Net loss attributable to Arconic Corporation (7) (17) (24) Earnings per share attributable to Arconic Corporation common shareholders: Basic $ (0.07) $ (0.15) $ (0.22) Diluted (0.07) (0.15) (0.22) Statement of Consolidated Operations for the nine months ended September 30, 2019: Cost of goods sold $ 4,810 $ 39 $ 4,849 Operating income 176 (39) 137 Income before income taxes 94 (39) 55 Provision for income taxes 55 (9) 46 Net income 39 (30) 9 Net income attributable to Arconic Corporation 39 (30) 9 Earnings per share attributable to Arconic Corporation common shareholders: Basic $ 0.35 $ (0.27) $ 0.08 Diluted 0.35 (0.27) 0.08 As Previously Reported Effect of Change As Recast Statement of Consolidated Comprehensive Income for the third quarter ended September 30, 2019: Comprehensive income $ 39 $ (17) $ 22 Comprehensive income attributable to Arconic Corporation 39 (17) 22 Statement of Consolidated Comprehensive Income for the nine months ended September 30, 2019: Comprehensive income $ 99 $ (30) $ 69 Comprehensive income attributable to Arconic Corporation 99 (30) 69 Consolidated Balance Sheet as of December 31, 2019: Inventories $ 820 $ 317 $ 1,137 Deferred income tax liabilities 87 72 159 Parent Company net investment 2,419 245 2,664 Statement of Consolidated Cash Flows for the nine months ended September 30, 2019: Net income $ 39 $ (30) $ 9 Deferred income taxes 20 (9) 11 (Increase) in inventories (69) 39 (30) The following table compares the amounts that were reported under average cost in the Consolidated Financial Statements as of and for the quarter and nine months ended September 30, 2020 with the amounts had they continued to be reported under LIFO: As Reported under As Computed under LIFO Effect of Change Statement of Consolidated Operations for the third quarter ended September 30, 2020: Cost of goods sold $ 1,218 $ 1,232 $ (14) Operating income 64 50 14 Income before income taxes 15 1 14 Provision for income taxes 10 6 4 Net income (loss) 5 (5) 10 Net income (loss) attributable to Arconic Corporation 5 (5) 10 Earnings per share attributable to Arconic Corporation common shareholders: Basic $ 0.05 $ (0.05) $ 0.10 Diluted 0.05 (0.05) 0.10 Statement of Consolidated Operations for the nine months ended September 30, 2020: Cost of goods sold $ 3,614 $ 3,605 $ 9 Operating income 126 135 (9) Loss before income taxes (40) (31) (9) Provision for income taxes 5 6 (1) As Reported under As Computed under LIFO Effect of Change Net loss (45) (37) (8) Net loss attributable to Arconic Corporation (45) (37) (8) Earnings per share attributable to Arconic Corporation common shareholders: Basic $ (0.41) $ (0.34) $ (0.07) Diluted (0.41) (0.34) (0.07) Statement of Consolidated Comprehensive Income for the third quarter ended September 30, 2020: Comprehensive income $ 85 $ 75 $ 10 Comprehensive income attributable to Arconic Corporation 85 75 10 Statement of Consolidated Comprehensive Income for the nine months ended September 30, 2020: Comprehensive income $ 94 $ 102 $ (8) Comprehensive income attributable to Arconic Corporation 94 102 (8) Consolidated Balance Sheet as of September 30, 2020: Inventories $ 901 $ 591 $ 310 Deferred income tax assets 296 366 (70) Additional capital 3,332 3,098 234 Accumulated deficit (91) (97) 6 Statement of Consolidated Cash Flows for the nine months ended September 30, 2020: Net loss $ (45) $ (37) $ (8) Deferred income taxes 28 29 (1) Decrease in inventories 197 188 9

Leases_

Leases​	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	Leases​ Arconic Corporation leases certain land and buildings, plant equipment, vehicles, and computer equipment, which have been classified as operating leases. Operating lease cost, which includes short-term leases and variable lease payments and approximates cash paid, was $14 and $15 for the third quarter of 2020 and 2019, respectively, and $43 and $47 for the nine-month period of 2020 and 2019, respectively. Right-of-use assets obtained in exchange for operating lease obligations in the 2020 third quarter and nine-month period were $6 and $38, respectively. Future minimum contractual operating lease obligations were as follows: ​ September 30, 2020 ​ December 31, 2019 2020 $ 11 $ 38 2021 38 29 2022 31 22 2023 24 17 2024 19 14 Thereafter 53 38 Total lease payments $ 176 $ 158 Less: imputed interest 33 29 Present value of lease liabilities $ 143 $ 129 The weighted-average remaining lease term and weighted-average discount rate for Arconic Corporation’s operating leases at September 30, 2020 and December 31, 2019 was 6.7 years and 6.7 years, respectively, and 5.9% and 6.0%, respectively.

Debt

Debt	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt	Debt In connection with the capital structure to be established at the time of the Separation, Arconic Corporation secured $1,200 in third-party indebtedness. On February 7, 2020, Arconic Corporation completed a Rule 144A (U.S. Securities Act of 1933, as amended) debt offering for $600 of 6.125% Senior Secured Second-Lien Notes due 2028 (the “2028 Notes”). The Company received $593 in net proceeds from the debt offering reflecting a discount to the initial purchasers of the 2028 Notes. Also, on March 25, 2020, Arconic Corporation entered into a credit agreement, which provided a $600 Senior Secured First-Lien Term Loan B Facility (variable rate and seven five The Company used a portion of the $1,168 in net proceeds from the aggregate indebtedness to make a $728 payment to ParentCo on April 1, 2020 to fund the transfer of certain net assets from ParentCo to Arconic Corporation in connection with the completion of the Separation (see Note A). The payment to ParentCo was calculated as the difference between (i) the $1,168 of net proceeds from the aggregate indebtedness and (ii) the difference between a beginning cash balance at the Separation Date of $500, as provided for in the Separation and Distribution Agreement, and the amount of cash held by Arconic Corporation Businesses at March 31, 2020 ($60 – the sum of this amount and the aggregate indebtedness in (i) equals the sum of Cash and cash equivalents and Restricted cash on the Company’s Combined Balance Sheet as of March 31, 2020). On April 2, 2020, Arconic Corporation borrowed $500, which was subject to an interest rate equal to the sum of the three-month LIBOR plus a 2.0% applicable margin, under the Credit Facility. This borrowing was a proactive measure taken by the Company to bolster its liquidity and preserve financial flexibility in light of uncertainties resulting from the COVID-19 outbreak (see Note A). On May 13, 2020, Arconic Corporation executed a refinancing of its existing Credit Agreement in order to provide improved financial flexibility. Arconic Corporation completed a Rule 144A (U.S. Securities Act of 1933, as amended) debt offering for $700 of 6.0% Senior Secured First-Lien Notes due 2025 (the “2025 Notes”). The Company received $691 in net proceeds from the debt offering reflecting a discount to the initial purchasers of the 2025 Notes. Additionally, Arconic Corporation entered into a credit agreement with a syndicate of lenders named therein and Deutsche Bank AG New York Branch, as administrative agent (the “ABL Credit Agreement”). The ABL Credit Agreement provides for a senior secured asset-based revolving credit facility in an aggregate principal amount of $800, including a letter of credit sub-facility and a swingline loan sub-facility (the “ABL Credit Facility”). In addition, the ABL Credit Facility includes an accordion feature allowing the Company to request one or more increases to the revolving commitments in an aggregate principal amount up to $350. Arconic Corporation used the net proceeds from the new indebtedness, together with cash on hand, to prepay in full the obligations outstanding under both the Term Loan ($600) and Credit Facility ($500) and to terminate in full the commitments under the Credit Agreement. Descriptions of the 2028 Notes, 2025 Notes, and ABL Credit Agreement are set forth below. In connection with the issuance of the 2028 Notes and the execution of the Credit Agreement, the Company paid $42 in discounts to the initial purchasers and/or upfront fees and costs (the “debt issuance costs”), of which $30 was attributable to Term Loan B and the Credit Facility. The debt issuance costs were initially deferred and were being amortized to interest expense over the respective terms of the 2028 Notes, Term Loan B, and the Credit Facility. In connection with the issuance of the 2025 Notes and the execution of the ABL Credit Agreement, the Company paid $15 in discounts to the initial purchasers and/or upfront fees and costs (the “new debt issuance costs”). As a result of applying both debt modification and debt extinguishment accounting, as appropriate based on the lender mix for each debt instrument, to the debt refinancing, the Company was required to write off $16 of the $30 in debt issuance costs and immediately expense $3 of the $15 in new debt issuance costs. This $19 was reported within Interest expense on the Company's Statement of Consolidated Operations. The remaining $14 in debt issuance costs continued to be deferred and the remaining $12 in new debt issuance costs were deferred; both are being amortized to interest expense over the respective terms of the 2025 Notes and the ABL Credit Agreement. Separately, in August 2012, ParentCo and the Iowa Finance Authority entered into a loan agreement for the proceeds from the issuance of $250 in Midwestern Disaster Area Revenue Bonds Series 2012 due 2042 (the “Bonds”). The Bonds were issued by the Iowa Finance Authority pursuant to the Heartland Disaster Tax Relief Act of 2008 for the purpose of financing all or part of the cost of acquiring, constructing, reconstructing, and renovating certain facilities (the “Project”) at Arconic Corporation’s rolling mill plant in Davenport, IA. The loan proceeds could only be used for this purpose and, therefore, were included on the Company’s Combined Balance Sheet for all periods prior to the Separation Date. In accordance with the Separation and Distribution Agreement, as well as a Second Supplemental Tax and Project Certificate and Agreement, dated March 31, 2020, to the Tax Exemption Certificate and Agreement, dated August 14, 2012, (collectively, the “Tax Agreement”), ParentCo remained the borrower associated with the Bonds and Arconic Corporation is the legal owner of the Davenport facility, including the Project. The Company has no financial obligations related to the future debt service of the Bonds but is required to continue to operate, and maintain the location of, the Project in accordance with the Tax Agreement. Accordingly, the $250 carrying value of the Bonds, as well as related accrued interest, was removed from Arconic Corporation’s Consolidated Balance Sheet in connection with the Separation. 2028 Notes —Interest on the 2028 Notes is paid semi-annually in February and August, which commenced August 15, 2020. Arconic Corporation has the option to redeem the 2028 Notes on at least 10 days, but not more than 60 days, prior notice to the holders of the 2028 Notes under multiple scenarios, including, in whole or in part, at any time or from time to time after February 14, 2023 at a redemption price specified in the indenture (up to 103.063% of the principal amount plus any accrued and unpaid interest in each case). At any time prior to February 15, 2023, the Company may redeem all or a part of the notes at a redemption price equal to 100% of the principal amount of the notes redeemed plus a “make-whole” redemption price determined as the greater of (1) 1.0% of the principal amount of such notes and (2) the excess, if any, of (a) the present value at the date of redemption of (i) 103.063% of the principal amount of such notes plus (ii) all required interest payments due on such notes (excluding accrued but unpaid interest to the date of redemption) through February 15, 2023, computed using a discount rate equal to, generally, the yield to maturity of United States Treasury securities with a constant maturity as of the date of redemption plus 50 basis points, over (b) the principal amount of such notes, as of, and accrued and unpaid interest, if any, to, but excluding, the date of redemption. Also, at any time prior to February 15, 2023, Arconic Corporation may, on one or more occasions, redeem up to 40% of the aggregate principal amount of the notes at a redemption price equal to 106.125% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date, with the net cash proceeds of certain equity offerings, if at least 60% of the original aggregate principal amount of the notes remains outstanding immediately after such redemption and the redemption occurs within 120 days of the date of such equity offering. Additionally, the 2028 Notes are subject to repurchase upon the occurrence of a change in control repurchase event (as defined in the indenture) at a repurchase price in cash equal to 101% of the aggregate principal amount of the 2028 Notes repurchased, plus any accrued and unpaid interest on the 2028 Notes repurchased. The 2028 Notes are senior secured obligations of Arconic Corporation and do not entitle the holders to any registration rights pursuant to a registration rights agreement. The Company does not intend to file a registration statement with respect to resales of or an exchange offer for the 2028 Notes. The 2028 Notes are guaranteed on a senior secured basis by Arconic Corporation and its subsidiaries that are guarantors (the “subsidiary guarantors” and, together with Arconic Corporation, the “guarantors”) under the ABL Credit Agreement (see below). Each of the subsidiary guarantors will be released from their 2028 Notes guarantees upon the occurrence of certain events, including the release of such guarantor from its obligations as a guarantor under the ABL Credit Agreement. The 2028 Notes indenture includes several customary affirmative covenants. Additionally, the 2028 Notes indenture contains several negative covenants, that, subject to certain exceptions, limit the Company’s ability to, among other things, (i) make investments, loans, advances, guarantees, and acquisitions, (ii) pay dividends on or make other distributions in respect of capital stock and make other restricted payments and investments (as defined in the 2028 Notes), (iii) sell or transfer certain assets, and (iv) create liens on assets to secure debt. The 2028 Notes rank equally in right of payment with all of Arconic Corporation’s existing and future senior indebtedness, including the facility under the ABL Credit Agreement (see below); rank senior in right of payment to any future subordinated obligations of Arconic Corporation; and are effectively subordinated to Arconic Corporation’s existing and future secured indebtedness that is secured on a first priority basis, including the 2025 Notes and the facility under the ABL Credit Agreement, to the extent of the value of property and assets securing such indebtedness. 2025 Notes— Interest on the 2025 Notes will be paid semi-annually in May and November, commencing November 15, 2020. Arconic Corporation has the option to redeem the 2025 Notes on at least 10 days, but not more than 60 days, prior notice to the holders of the 2025 Notes under multiple scenarios, including, in whole or in part, at any time or from time to time after May 14, 2022 at a redemption price specified in the indenture (up to 103.0% of the principal amount plus any accrued and unpaid interest in each case). At any time prior to May 15, 2022, the Company may redeem all or a part of the notes at a redemption price equal to 100% of the principal amount of the notes redeemed plus a “make-whole” redemption price determined as the greater of (1) 1.0% of the principal amount of such notes and (2) the excess, if any, of (a) the present value at the date of redemption of (i) 103.0% of the principal amount of such notes plus (ii) all required interest payments due on such notes (excluding accrued but unpaid interest to the date of redemption) through May 15, 2022, computed using a discount rate equal to, generally, the yield to maturity of United States Treasury securities with a constant maturity as of the date of redemption plus 50 basis points, over (b) the principal amount of such notes, as of, and accrued and unpaid interest, if any, to, but excluding, the date of redemption. Also, at any time prior to May 15, 2022, Arconic Corporation may, on one or more occasions, redeem up to 40% of the aggregate principal amount of the notes at a redemption price equal to 106.0% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the redemption date, with the net cash proceeds of certain equity offerings, if at least 60% of the original aggregate principal amount of the notes remains outstanding immediately after such redemption and the redemption occurs within 120 days of the date of such equity offering. Additionally, the 2025 Notes are subject to repurchase upon the occurrence of a change in control repurchase event (as defined in the indenture) at a repurchase price in cash equal to 101% of the aggregate principal amount of the 2025 Notes repurchased, plus any accrued and unpaid interest on the 2025 Notes repurchased. The 2025 Notes are senior secured obligations of Arconic Corporation and do not entitle the holders to any registration rights pursuant to a registration rights agreement. The Company does not intend to file a registration statement with respect to resales of or an exchange offer for the 2025 Notes. The 2025 Notes are guaranteed on a senior secured basis by Arconic Corporation and its subsidiaries that are guarantors (the “subsidiary guarantors” and, together with Arconic Corporation, the “guarantors”) under the ABL Credit Agreement (see below). Each of the subsidiary guarantors will be released from their 2025 Notes guarantees upon the occurrence of certain events, including the release of such guarantor from its obligations as a guarantor under the ABL Credit Agreement. The 2025 Notes indenture includes several customary affirmative covenants. Additionally, the 2025 Notes indenture contains several negative covenants, that, subject to certain exceptions, limit the Company’s ability to, among other things, (i) pay dividends on or make other distributions in respect of capital stock and make other restricted payments and investments (as defined in the 2025 Notes), (ii) sell or transfer certain assets, (iii) incur indebtedness, and (iv) create liens on assets to secure debt. The 2025 Notes are secured on a first priority basis by certain defined collateral (generally consisting of the Company’s and the Guarantors’ equipment, material owned U.S. real property, intellectual property, certain stock, and other tangible and intangible personal property, in each case, subject to certain exceptions) and on a second priority basis by certain other assets (generally consisting of substantially all of the accounts receivable, inventory, deposit accounts, securities accounts, commodities accounts, and cash assets of the Company and the Guarantors, and the proceeds thereof). ABL Credit Agreement— Availability under the ABL Credit Facility is subject to a quarterly borrowing base calculation, generally based upon a set percentage of eligible accounts receivable and inventory, less customary reserves. During the 2020 third quarter, the calculated available balance was $681. On October 21, 2020, the calculated available balance for the 2020 fourth quarter was determined to be $678. The ABL Credit Facility is scheduled to mature on May 13, 2025, unless extended or earlier terminated in accordance with the ABL Credit Agreement. Under the provision of the ABL Credit Agreement, Arconic Corporation will pay a quarterly commitment fee ranging from 0.250% to 0.375% (based on Arconic Corporation’s leverage ratio) per annum on the unused portion of the ABL Credit Facility, which will be determined based on the Company’s average daily utilization. The ABL Credit Facility was undrawn as of September 30, 2020 and no amounts were borrowed since inception. The ABL Credit Facility is subject to an interest rate for U.S. dollar borrowings equal to an applicable margin plus, at the Company’s option, of either (a) base rate (“ABR”) determined by reference to the highest of (1) Deutsche Bank AG New York Branch’s “prime rate,” (2) the greater of the federal funds effective rate and the overnight bank funding rate, plus 0.5%, and (3) the one month adjusted LIBO Rate, plus 1% per annum or (b) an adjusted LIBO Rate (which will not be less than 0.75% per annum) (“LIBOR”). The applicable margin for the ABL Credit Facility through June 30, 2021 is (a) 1.25% for ABR loans and (b) 2.25% for LIBOR loans. Thereafter, the applicable margin for the ABL Credit Facility will be (a) 0.75% to 1.25% per annum for ABR loans and (b) 1.75% per annum to 2.25% per annum for LIBOR loans based on the average daily excess availability (as defined under the ABL Credit Agreement). Accordingly, the interest rates for the ABL Credit Facility will fluctuate based on changes in the ABR, LIBOR, and/or future changes in the average daily excess availability. All obligations under the ABL Credit Facility are unconditionally guaranteed, jointly and severally, by substantially all of the direct and indirect wholly-owned material subsidiaries of the Company that are organized under the laws of the United States, any state thereof or the District of Columbia, subject to certain exceptions (collectively, the “Guarantors”). The Company and the Guarantors entered into a guarantee under the ABL Credit Agreement concurrently with the effectiveness of the ABL Credit Agreement. Subject to certain limitations, the ABL Credit Facility is secured on a first priority basis by certain defined collateral (generally consisting of substantially all of the accounts receivable, inventory, deposit accounts, securities accounts, commodities accounts, and cash assets of the Company and the Guarantors, and the proceeds thereof) and on a second-priority basis by certain defined collateral under the 2025 Notes (generally consisting of the Company and the Guarantors’ equipment, material owned U.S. real property, intellectual property, certain stock, and other tangible and intangible personal property, in each case, subject to exceptions as defined in the 2025 Notes). The Company and the Guarantors entered into collateral agreements concurrently with the effectiveness of the ABL Credit Agreement. The ABL Credit Facility contains certain affirmative and negative covenants customary for financings of this type that, among other things, limit the Company’s and its subsidiaries’ ability to incur additional indebtedness or liens, to dispose of assets, to make certain fundamental changes, to enter into restrictive agreements, to make certain investments, loans, advances, guarantees and acquisitions, to prepay certain indebtedness and to pay dividends, to make other distributions or redemptions/repurchases, in respect of the Company’s and its subsidiaries’ equity interests, to engage in transactions with affiliates and to amend certain material documents. In addition, the ABL Credit Facility contains a financial maintenance covenant applicable to any fiscal quarter in which the excess availability is less than the greater of (a) 10% of the lesser of (x) the aggregate amount of the commitments under the ABL Credit Facility and (y) the borrowing base and (b) $50. In such circumstances, until such time as excess availability shall have exceeded such threshold for at least 30 consecutive days, the Company would be required to maintain a fixed charge coverage ratio of not less than 1.00 to 1.00. The ABL Credit Facility also requires the Company and its subsidiaries to maintain substantially all of the Company’s cash in accounts that are subject to the control of the agent, which control becomes applicable when (a) an event of default under the facility occurs and is continuing until the first day thereafter on which no event of default shall exist or (b) excess availability is less than the greater of (i) 12.5% of the lesser of (x) the aggregate amount of the commitments under the ABL Credit Facility and (y) the borrowing base or (ii) $62.5 for five consecutive business days until the first day thereafter on which excess availability shall have exceeded such threshold for at least 30 consecutive days. The ABL Credit Facility contains customary events of default, including with respect to a failure to make payments thereunder, cross-default and cross-acceleration, certain bankruptcy and insolvency events, and customary change of control events. Fair Value— Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value hierarchy distinguishes between (i) market participant assumptions developed based on market data obtained from independent sources (observable inputs) and (ii) an entity’s own assumptions about market participant assumptions developed based on the best information available in the circumstances (unobservable inputs). The fair value hierarchy consists of three broad levels, which gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy are described below: • Level 1—Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. • Level 2—Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly, including quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in markets that are not active; inputs other than quoted prices that are observable for the asset or liability (e.g., interest rates); and inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3—Inputs that are both significant to the fair value measurement and unobservable. As of September 30, 2020, the combined carrying value and fair value of the 2028 Notes and 2025 Notes were $1,277 and $1,365, respectively. The fair value amounts for the 2028 Notes and 2025 Notes were based on quoted market prices for public debt and were classified in Level 2 of the fair value hierarchy.

Acquisitions and Divestitures

Acquisitions and Divestitures	9 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Acquisitions and Divestitures	Acquisitions and Divestitures​ On February 1, 2020, Arconic Corporation completed the sale of its aluminum rolling mill (specialty foil and sheet products) in Itapissuma, Brazil to Companhia Brasileira de Alumínio for a net $46 in cash, resulting in a loss of $59 (pretax). In 2019, Arconic Corporation recognized a charge of $53 (pretax), consisting of $59 (pretax) in the 2019 third quarter for the non-cash impairment of the carrying value of the rolling mill’s net assets, primarily properties, plants, and equipment, as a result of entering into an agreement in August 2019 to sell this rolling mill, and a $6 credit in the 2019 fourth quarter to reflect subsequent changes in both foreign currency exchange rates and working capital balances. Additionally, in the 2020 first quarter, Arconic Corporation recognized a charge of $6 (pretax) for further necessary adjustments upon completion of the divestiture. Each of these amounts were recorded in Restructuring and other charges (see Note E) on the Company’s Statement of Consolidated Operations in the respective reporting periods. This transaction remains subject to certain post-closing adjustments as defined in the agreement. Prior to the divestiture, this rolling mill’s operating results and assets and liabilities were reported in the Rolled Products segment. The rolling mill generated third-party sales of $143, $179, and $162 in 2019, 2018, and 2017, respectively, and, at the time of divestiture, had approximately 500 employees. On March 1, 2020, Arconic Corporation completed the sale of its hard alloy extrusions plant in South Korea to SeAH Besteel Corporation for a net $55 in cash, resulting in a gain of $31 (pretax), which was recorded in Restructuring and other charges (see Note E) on the accompanying Statement of Consolidated Operations. The gain is net of a $6 write-off of related goodwill. In the 2020 second quarter, Arconic Corporation received an additional $1 in cash as a result of a post-closing adjustment, which was previously contemplated in the aforementioned gain. This transaction is no longer subject to post-closing adjustments. Prior to the divestiture, this plant’s operating results and assets and liabilities were reported in the Extrusions segment. The extrusions plant generated third-party sales of $51, $53, and $50 in 2019, 2018, and 2017, respectively, and, at the time of divestiture, had approximately 160 employees.

Contingencies and Commitments_

Contingencies and Commitments​	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Commitments​	Contingencies and Commitments​ Unless specifically described to the contrary, all matters within Note O are the full responsibility of Arconic Corporation pursuant to the Separation and Distribution Agreement (see Note A). Additionally, the Separation and Distribution Agreement provides for cross-indemnities between the Company and Howmet Aerospace for claims subject to indemnification. Contingencies Environmental Matters. Arconic Corporation participates in environmental assessments and cleanups at several 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, among others, the nature and extent of contamination, changes in remedial requirements, and technological changes. Arconic Corporation’s remediation reserve balance was $181 and $208 (of which $97 and $83, respectively, was classified as a current liability) at September 30, 2020 and December 31, 2019, respectively, and reflects the most probable costs to remediate identified environmental conditions for which costs can be reasonably estimated. Additionally, Accounts payable, trade includes unpaid invoices of $22 related to environmental remediation projects as of December 31, 2019. In the 2020 third quarter and nine-month period, the remediation reserve was increased by $1 and reduced by $3, respectively. The change to the remediation reserve in both periods includes a charge of $1 (recorded in Cost of goods sold) due to incremental estimated expenditures associated with active remediation systems and/or monitoring and inspection programs at several sites. Additionally, in the 2020 nine-month period, the change to the remediation reserve includes the reversal of a $5 liability (a credit was recorded in Restructuring and other charges – see Note E) previously established by ParentCo, as the underlying obligation no longer exists based on an assessment completed by Arconic Corporation management, and a charge of $1 (recorded in Restructuring and other charges – see Note E) to establish a liability related to the divestiture of a rolling mill in Brazil (see Note N). Payments related to remediation expenses applied against the reserve were $33 and $54 in the 2020 third quarter and nine-month period, respectively. These amounts include expenditures currently mandated, as well as those not required by any regulatory authority or third party. The change in the reserve in the 2020 nine-month period also reflects both an increase of $13 for obligations transferred from ParentCo on April 1, 2020 in connection with the Separation (see below) and a decrease of $5 for other items. The Separation and Distribution Agreement includes provisions for the assignment or allocation of environmental liabilities between Arconic Corporation and Howmet Aerospace, including certain remediation obligations associated with environmental matters. In general, the respective parties are responsible for the environmental matters associated with their operations, and with the properties and other assets assigned to each. Additionally, the Separation and Distribution Agreement lists environmental matters with a shared responsibility between the two companies with an allocation of responsibility and the lead party responsible for management of each matter. For matters assigned to Arconic Corporation and Howmet Aerospace under the Separation and Distribution Agreement, the companies have agreed to indemnify each other in whole or in part for environmental liabilities arising from operations prior to the Separation Date. The following description provides details regarding the current status of one reserve, which represents the majority of the Company’s total remediation reserve balance, related to a current Arconic Corporation site. Massena West, NY— Arconic Corporation has an ongoing remediation project related to the Grasse River, which is adjacent to the Company’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. Arconic Corporation completed the final design phase of the project, which was approved by the EPA in March 2019. Following the EPA’s approval, the actual remediation fieldwork commenced. In June 2019, Arconic Corporation increased the reserve balance by $25 due to changes required in the EPA-approved remedial design and post-construction monitoring. These changes were necessary due to several items, the majority of which relates to navigation issues identified by a local seaway development company. Accordingly, the EPA requested an addendum to the final remedial design be submitted to address these issues. The proposed remedy is to dredge certain of the sediments originally identified for capping in the affected areas of the Grasse River, resulting in incremental project costs. The EPA approved the proposal in April 2020. As the project progresses, further changes to the reserve may be required due to factors such as, among others, additional changes in remedial requirements, increased site restoration costs, and incremental ongoing operation and maintenance costs. At September 30, 2020 and December 31, 2019, the reserve balance associated with this matter was $131 and $171, respectively. Additionally, Accounts payable, trade includes unpaid invoices of $21 related to this project as of December 31, 2019. The majority of the remaining expenditures related to the project are expected to occur between the remainder of 2020 and 2022. Litigation. All references to ParentCo in the matters described under this section Litigation refer to Arconic Inc. only and do not include its subsidiaries, except as otherwise stated. Reynobond PE —On June 13, 2017, the Grenfell Tower in London, U.K. caught fire resulting in fatalities, injuries, and damage. A French subsidiary of Arconic Corporation (of ParentCo at that time), 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 facade installer, who then completed and installed the system under the direction of the general contractor. Neither ParentCo 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 Metropolitan Police Service (the “Police”), a Public Inquiry by the British government, and a consumer protection inquiry by a French public authority. The Public Inquiry was announced by the U.K. Prime Minister on June 15, 2017 and subsequently was authorized to examine the circumstances leading up to and surrounding the Grenfell Tower fire in order to make findings of fact and recommendations to the U.K. Government on matters such as the design, construction, and modification of the building, the role of relevant public authorities and contractors, the implications of the fire for the adequacy and enforcement of relevant regulations, arrangements in place for handling emergencies, and the handling of concerns from residents, among other things. Hearings for Phase 1 of the Public Inquiry began on May 21, 2018 and concluded on December 12, 2018. Phase 2 hearings of the Public Inquiry began in early 2020, following which a final report will be written and subsequently published. As Phase 2 of the public inquiry resumed in July after a hiatus due to the COVID-19 pandemic, the testimony has supported AAP SAS’s position that the choice of materials and the responsibility of ensuring compliance of the cladding system with relevant U.K. building code and regulations was with those individuals or entities who designed and installed the cladding system such as the architects, fabricators, contractors and building owners. The ongoing hearings in the U.K. have revealed serious doubts about whether these third parties had the necessary qualifications or expertise to carry out the refurbishment work at Grenfell Tower, adequately oversaw the process, conducted the required fire safety testing or analysis, or otherwise complied with their obligations under U.K. regulations. AAP SAS is participating as a Core Participant in the Public Inquiry and is also cooperating with the ongoing parallel investigation by the Police. Arconic Corporation does not sell and ParentCo previously stopped selling the PE product for architectural use on buildings. Given the preliminary nature of these investigations and the uncertainty of potential future litigation, Arconic Corporation 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. United Kingdom Litigation. Multiple claimant groups comprised of survivors and estates of decedents of the Grenfell Tower fire have filed claims in the U.K. arising from that fire, including as follows: • On June 12, 2020, four claimants represented by Birnberg Peirce Ltd filed suit against AAP SAS. • On June 12, 2020, two claimants represented by Howe & Co Solicitors filed suit against AAP SAS. • On June 26, 2020, three claimants represented by Russell-Cooke LLP filed suit against AAP SAS. Multiple claimant groups comprised of emergency responders who attended the Grenfell Tower fire have also filed claims against AAP SAS arising from that fire, including as follows: • On June 11, 2020, 80 firefighters represented by Thompsons Solicitors filed suit against AAP SAS, as well as the Royal Borough of Kensington and Chelsea, the Royal Borough of Kensington and Chelsea Tenant Management Organisation Ltd, Celotex Ltd, Exova (U.K.) Ltd, Rydon Maintenance Ltd, Studio E Architects Ltd, Harley Facades Ltd, CEP Architectural Facades Ltd, CS Stokes & Associates Ltd, and the London Fire Commissioner. Since then, another 18 firefighters have sought to be added to the suit. • On June 12, 2020, 27 police officers represented by Penningtons Manches Cooper LLP filed suit against AAP SAS, as well as the Royal Borough of Kensington and Chelsea, the Royal Borough of Kensington and Chelsea Tenant Management Organisation Ltd, Celotex Ltd, Exova (U.K.) Ltd, Rydon Maintenance Ltd, Studio E Architects Ltd, Harley Facades Ltd, CEP Architectural Facades Ltd, CS Stokes & Associates Ltd, London Fire Commissioner, and the Commissioner of the Police of the Metropolis. Since then, some claimants have withdrawn and others have sought to be added to the suit. Currently, there are 37 police officer claimants. • On June 12, 2020, two firefighters represented by Pattinson and Brewer filed suit against AAP SAS, as well as the Royal Borough of Kensington and Chelsea, the Royal Borough of Kensington and Chelsea Tenant Management Organisation Ltd, Celotex Ltd, Exova (U.K.) Ltd, Rydon Maintenance Ltd, Studio E Architects Ltd, Harley Facades Ltd, CEP Architectural Facades Ltd, CS Stokes & Associates Ltd, and the London Fire Commissioner. A third firefighter, also represented by Pattinson and Brewer, brought a claim against the same defendants on June 15, 2020. One of the original firefighter claimants has now withdrawn from the suit. All of these claims have been filed in the High Court in London. On October 2, 2020, the High Court ordered that (a) the suits of the survivors and estates of decedents be stayed until a hearing to be scheduled by the High Court after April 13, 2021; and (b) that the suits of emergency responders be stayed until a hearing to be scheduled by the High Court after May 31, 2021. Given the preliminary nature of these matters and the uncertainty of litigation, Arconic Corporation 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 in any of the above-referenced disputes. Behrens et al. v. Arconic Inc. et al. On June 6, 2019, 247 plaintiffs comprised of survivors and estates of decedents of the Grenfell Tower fire filed a complaint against “Arconic Inc., Alcoa Inc., and Arconic Architectural Products, LLC” (collectively, for purposes of the description of such proceeding, the “ParentCo Defendants”), as well as Saint-Gobain Corporation, d/b/a Celotex and Whirlpool Corporation, in the Court of Common Pleas of Philadelphia County. The complaint alleges claims under Pennsylvania state law for products liability and wrongful death related to the fire. In particular, the plaintiffs allege that the ParentCo Defendants knowingly supplied a dangerous product (Reynobond PE) for installation on the Grenfell Tower despite knowing that Reynobond PE was unfit for use above a certain height. The ParentCo Defendants removed the case to the United States District Court for the Eastern District of Pennsylvania on June 19, 2019. On August 29, 2019, the ParentCo Defendants moved to dismiss the complaint on the bases, among other things, that: (i) the case should be heard in the United Kingdom, not the United States; (ii) there is no jurisdiction over necessary parties; and (iii) Pennsylvania product liability law does not apply to manufacture and sale of product overseas. On December 23, 2019, the Court issued an order denying the motion to dismiss the complaint on bases (ii) and (iii) suggesting a procedure for limited discovery followed by further briefing on those subjects. On September 16, 2020, the Court issued an order granting Defendants’ motion to dismiss on forum non conveniens grounds, determining that the United Kingdom, and not the United States, is the appropriate place for plaintiffs to bring their case. Plaintiffs subsequently filed a motion for reconsideration and Defendants are preparing a response. Given the preliminary nature of this matter and the uncertainty of litigation, Arconic Corporation 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. Howard v. Arconic Inc. et al. 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 ParentCo and Klaus Kleinfeld. A related purported class action complaint was filed in the United States District Court for the Western District of Pennsylvania on September 15, 2017, under the caption Sullivan v. Arconic Inc. et al. , against ParentCo, three former ParentCo executives, several current and former ParentCo directors, and banks that acted as underwriters for ParentCo’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 alleged 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 alleged that between November 4, 2013 and June 23, 2017 ParentCo and Kleinfeld made false and misleading statements and failed to disclose material information about ParentCo’s commitment to safety, business and financial prospects, and the risks of the Reynobond PE product, including in ParentCo’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, its 2016 Annual Highlights Report, and on its official website. The consolidated amended complaint sought, 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. On June 21, 2019, the Court granted the defendants’ motion to dismiss in full, dismissing the consolidated amended complaint in its entirety without prejudice. On July 23, 2019, the lead plaintiffs filed a second amended complaint. The second amended complaint alleges generally the same claims as the consolidated amended complaint with certain additional allegations, as well as claims that the risk factors set forth in the registration statement for the Preferred Offering were inadequate and that certain additional statements in the sources identified above were misleading. The second amended complaint seeks, among other things, unspecified compensatory damages and an award of attorney and expert fees and expenses. On September 11, 2019, all defendants moved to dismiss the second amended complaint. Plaintiffs’ opposition to that motion was filed on November 1, 2019 and all defendants filed a reply brief on November 26, 2019. On June 22, 2020, counsel for Arconic and the individual defendants filed a letter apprising the Court of a recent decision by the Third Circuit and discussing its relevance to the pending motion to dismiss. Pursuant to an Order by the Court directing the plaintiffs to respond to this letter, the plaintiffs filed a letter response on July 9, 2020. The motion to dismiss remains pending. Given the preliminary nature of this matter and the uncertainty of litigation, Arconic Corporation 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. Raul v. Albaugh, et al. On June 22, 2018, a derivative complaint was filed nominally on behalf of ParentCo by a purported ParentCo stockholder against the then members of ParentCo’s Board of Directors and Klaus Kleinfeld and Ken Giacobbe, naming ParentCo 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 and second 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, as amended, 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 Police and on July 23, 2018, the Court approved the stay. Given the preliminary nature of this matter and the uncertainty of litigation, Arconic Corporation 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. General. While Arconic Corporation believes that all the above referenced Reynobond PE cases are without merit and intends to challenge them vigorously, there can be no assurances regarding the ultimate resolution of these matters. General. In addition to the matters described above, various other lawsuits, claims, and proceedings have been or may be instituted or asserted against Arconic Corporation, 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 is not readily determinable because of the considerable uncertainties that exist. Accordingly, it is possible that the Company’s liquidity or results of operations in a reporting 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 Arconic Corporation.

Subsequent Events_

Subsequent Events​	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events​Management evaluated all activity of Arconic Corporation 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 described below.In October 2018, Arconic Corporation 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, subject to post-closing adjustments, plus additional contingent consideration of up to $50. The contingent consideration relates to the achievement of various milestones associated with operationalizing the rolling mill equipment within 36 months of the transaction closing date. Through 2019, the Company received contingent consideration of $25. On October 30, 2020, the Company received the remaining contingent consideration of $25.

Recently Adopted and Recently_2

Recently Adopted and Recently Issued Accounting Guidance (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Recent Accounting Guidance	Adopted On January 1, 2020, Arconic Corporation adopted changes issued by the Financial Accounting Standards Board (FASB) to credit losses. This guidance added a new impairment model (known as the current expected credit loss (CECL) model), which is based on expected losses rather than incurred losses. Under this model, an entity is required to recognize an allowance equivalent to 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. This model does not have a minimum threshold for recognition of impairment losses and requires the measurement of expected credit losses on assets that have a low risk of loss. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements. This guidance will need to be considered in future assessments of credit losses. Issued In March 2020, the FASB issued guidance that provides optional expedients and exceptions for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. These expedients and exceptions may be used when applying GAAP, if certain criteria are met, to contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of such reform. The purpose of this guidance is to provide relief to entities from experiencing unintended accounting and/or financial reporting outcomes or consequences due to reference rate reform. This guidance became effective immediately on March 12, 2020 and may be applied prospectively to contract modifications made and hedging relationships entered into or evaluated on or before December 31, 2022, after which time the expedients and exceptions expire. As of September 30, 2020, the Company has not experienced any unintended outcomes or consequences of reference rate reform that would necessitate the adoption of this guidance. Additionally, the Company will not need to consider the application of this guidance related to its credit agreement, which is scheduled to mature on May 13, 2025 and provides a credit facility that is referenced to LIBOR in certain borrowing situations (see Note M), as the terms of such agreement currently provide for a replacement rate if LIBOR is discontinued by the end of 2021 as expected. That said, management will continue to closely monitor all potential instances of reference rate reform to determine if adoption of this guidance becomes necessary in the future.
Basis of Accounting, Policy	Basis of Presentation. The Consolidated Financial Statements of Arconic Corporation are prepared in conformity with GAAP. In accordance with GAAP, certain situations require management to make estimates based on judgments and assumptions, which may affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements. These estimates are based on historical experience and, in some cases, assumptions based on current and future market experience, including considerations related to COVID-19. Management has made its best estimates using all relevant information available at the time, but it is possible that these estimates will differ from actual results and affect the Consolidated Financial Statements in future periods and potentially require adverse adjustments to the recoverability of goodwill and long-lived assets, the realizability of deferred tax assets and other judgments and estimations and assumptions that may be impacted by COVID-19.
Consolidation, Policy	Principles of Consolidation. The Consolidated Financial Statements of Arconic Corporation include the accounts of Arconic Corporation and companies in which Arconic Corporation has a controlling interest. Intercompany transactions have been eliminated. Prior to the Separation Date, Arconic Corporation did not operate as a separate, standalone entity. Arconic Corporation’s operations were included in ParentCo’s financial results. Accordingly, for all periods prior to the Separation Date, the accompanying Consolidated Financial Statements were prepared from ParentCo’s historical accounting records and were presented on a standalone basis as if the Arconic Corporation Businesses had been conducted independently from ParentCo. Such Consolidated Financial Statements include the historical operations that were considered to comprise the Arconic Corporation Businesses, as well as certain assets and liabilities that were historically held at ParentCo’s corporate level but were specifically identifiable or otherwise attributable to Arconic Corporation. ParentCo’s net investment in these operations was reflected as Parent Company net investment on the accompanying Consolidated Financial Statements. All significant transactions and accounts within Arconic Corporation were eliminated. All significant intercompany transactions between ParentCo and Arconic Corporation were included within Parent Company net investment on the accompanying Consolidated Financial Statements.
Costs Associated with Exit or Disposal Activities or Restructurings, Policy	Cost Allocations. The description and information on cost allocations is applicable for all periods included in the Consolidated Financial Statements prior to the Separation Date. The Consolidated Financial Statements of Arconic Corporation include general corporate expenses of ParentCo that were not historically charged to the Arconic Corporation Businesses for certain support functions that were provided on a centralized basis, such as expenses related to finance, audit, legal, information technology, human resources, communications, compliance, facilities, employee benefits and compensation, and research and development activities. These general corporate expenses were included on the accompanying Statement of Consolidated Operations within Cost of goods sold, Selling, general administrative and other expenses, and Research and development expenses. These expenses were allocated to Arconic Corporation on the basis of direct usage when identifiable, with the remainder allocated based on the Arconic Corporation Businesses’ segment revenue as a percentage of ParentCo’s total segment revenue, as reported in the respective periods. All external debt not directly attributable to Arconic Corporation was excluded from the accompanying Consolidated Balance Sheet. Financing costs related to these debt obligations were allocated to Arconic Corporation based on the ratio of capital invested by ParentCo in the Arconic Corporation Businesses to the total capital invested by ParentCo in both the Arconic Corporation Businesses and the Howmet Aerospace Businesses, and were included on the accompanying Statement of Consolidated Operations within Interest expense.

The Separation and Basis of P_2

The Separation and Basis of Presentation (Tables)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Costs Allocations	The following table reflects the allocations described above: Third quarter ended September 30, Nine months ended September 30, 2020 2019 ​ 2020 2019 Cost of goods sold (1) $ — $ 4 ​ $ — $ 11 Selling, general administrative, and other expenses (2) — 27 ​ 25 80 Research and development expenses — 1 ​ — 8 Provision for depreciation and amortization — 4 ​ 1 9 Restructuring and other charges (E) — 2 ​ 2 5 Interest expense — 29 ​ 28 86 Other expenses (income), net (F) — 1 ​ (5) 4 ​ _____________________ (1) For all periods presented, amount principally relates to an allocation of expenses for ParentCo’s retained pension and other postretirement benefit obligations associated with closed and sold operations. ​ (2) In the 2020 nine-month period and the 2019 third quarter and nine-month period, amount includes an allocation of $18, $13, and $23, respectively, for costs incurred by ParentCo associated with the Separation (see above).

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Schedule of Revenue by Major End Market Served	The following table disaggregates revenue by major end market served. Third quarter ended September 30, Rolled Building and Extrusions Total 2020 ​ ​ ​ ​ Ground Transportation $ 493 $ — $ 25 $ 518 Building and Construction 42 241 — 283 Aerospace 107 — 44 151 Industrial Products and Other 252 — 13 265 Packaging 198 — — 198 Total end-market revenue $ 1,092 $ 241 $ 82 $ 1,415 2019 ​ ​ ​ ​ Ground Transportation $ 592 $ — $ 26 $ 618 Building and Construction 47 282 — 329 Aerospace 243 — 68 311 Industrial Products and Other 279 — 32 311 Packaging 236 — — 236 Total end-market revenue $ 1,397 $ 282 $ 126 $ 1,805 Nine months ended September 30, ​ Rolled Building and Extrusions Total 2020 ​ ​ ​ ​ ​ Ground Transportation ​ $ 1,242 $ — $ 62 $ 1,304 Building and Construction ​ 110 727 — 837 Aerospace ​ 505 — 183 688 Industrial Products and Other ​ 766 — 51 817 Packaging ​ 571 — — 571 Total end-market revenue ​ $ 3,194 $ 727 $ 296 $ 4,217 2019 ​ ​ ​ ​ Ground Transportation $ 1,878 $ — $ 88 $ 1,966 Building and Construction 149 855 — 1,004 Aerospace 754 — 221 975 Industrial Products and Other 826 — 111 937 Packaging 687 — — 687 Total end-market revenue $ 4,294 $ 855 $ 420 $ 5,569

Segment and Related Informati_2

Segment and Related Information​ (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	The operating results of the Company’s reportable segments were as follows (differences between segment totals and consolidated amounts are in Corporate): Third quarter ended September 30, ​ Rolled Building and Extrusions Total 2020 ​ ​ ​ ​ ​ Sales: ​ ​ ​ ​ ​ Third-party sales-unrelated party ​ $ 1,073 $ 241 $ 77 $ 1,391 Third-party sales-related party ​ 19 — 5 24 Intersegment sales ​ 3 — 1 4 Total sales ​ $ 1,095 $ 241 $ 83 $ 1,419 Segment Adjusted EBITDA (1) ​ $ 138 $ 40 $ (6) $ 172 Provision for depreciation and amortization ​ $ 48 $ 5 $ 6 $ 59 2019 ​ Sales: ​ Third-party sales-unrelated party ​ $ 1,366 $ 282 $ 116 $ 1,764 Third-party sales-related party ​ 31 — 10 41 Intersegment sales ​ 4 — 1 5 Total sales ​ $ 1,401 $ 282 $ 127 $ 1,810 Segment Adjusted EBITDA (1),(2) ​ $ 160 $ 39 $ (8) $ 191 Provision for depreciation and amortization ​ $ 46 $ 4 $ 7 $ 57 Nine months ended September 30, ​ Rolled Building and Extrusions Total 2020 ​ ​ ​ ​ ​ Sales: ​ ​ ​ ​ ​ Third-party sales-unrelated party ​ $ 3,144 $ 727 $ 265 $ 4,136 Third-party sales-related party ​ 50 — 31 81 Intersegment sales ​ 14 — 1 15 Total sales ​ $ 3,208 $ 727 $ 297 $ 4,232 Segment Adjusted EBITDA (1) ​ $ 388 $ 107 $ (12) $ 483 Provision for depreciation and amortization ​ $ 147 $ 14 $ 18 $ 179 2019 ​ Sales: ​ Third-party sales-unrelated party ​ $ 4,193 $ 855 $ 379 $ 5,427 Third-party sales-related party ​ 101 — 41 142 Intersegment sales ​ 20 — 1 21 Total sales ​ $ 4,314 $ 855 $ 421 $ 5,590 Segment Adjusted EBITDA (1),(2) ​ $ 499 $ 96 $ (6) $ 589 Provision for depreciation and amortization ​ $ 139 $ 14 $ 22 $ 175 The following table reconciles total Segment Adjusted EBITDA to consolidated net income (loss) attributable to Arconic Corporation: Third quarter ended September 30, Nine months ended September 30, 2020 2019 2020 2019 Total Segment Adjusted EBITDA (1),(2) $ 172 $ 191 $ 483 $ 589 Unallocated amounts: Corporate expenses (1),(3) (6) (10) (15) (43) Stock-based compensation expense (6) (10) (18) (28) Metal price lag (4) (16) (10) (30) (33) Provision for depreciation and amortization (63) (63) (191) (190) Restructuring and other charges (E) (3) (64) (61) (104) Other (1),(5) (14) (12) (42) (54) Operating income (2) 64 22 126 137 Interest expense (22) (29) (97) (86) Other (expenses) income, net (1) (F) (27) — (69) 4 Provision for income taxes (2) (10) (17) (5) (46) Net income attributable to noncontrolling interest — — — — Consolidated net income (loss) attributable to Arconic Corporation (2) $ 5 $ (24) $ (45) $ 9 ________________ ​ (1) In preparation for the Separation, effective January 1, 2020, certain U.S. defined benefit pension and other postretirement plans previously sponsored by ParentCo were separated into standalone plans for both Arconic Corporation and Howmet Aerospace. Additionally, effective April 1, 2020, Arconic Corporation assumed a portion of the obligations associated with certain non-U.S. defined benefit pension plans that included participants related to both the Arconic Corporation Businesses and the Howmet Aerospace Businesses, as well as legacy defined benefit pension plans assigned to the Company as a result of the Separation. As a result, beginning in the first quarter of 2020 for these U.S. plans and in the second quarter of 2020 for these non-U.S. plans, Arconic Corporation applied defined benefit plan accounting resulting in benefit plan expense being recorded in operating income (service cost) and nonoperating income (nonservice cost). In all historical periods prior to these respective timeframes, Arconic Corporation was considered a participating employer in ParentCo’s defined benefit plans and, therefore, applied multiemployer plan accounting resulting in the Company’s share of benefit plan expense being recorded entirely in operating income. Also, Arconic Corporation is the plan sponsor of certain other non-U.S. defined benefit plans that contain participants related only to the Arconic Corporation Businesses and, therefore, the related benefit plan expense was recorded in accordance with defined benefit plan accounting in all periods presented. The following table presents the total benefit plan expense (excluding settlements and curtailments) recorded by Arconic Corporation based on the foregoing in each period presented: Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 2020 ​ 2019 Segment Adjusted EBITDA: Rolled Products $ (5) $ (16) $ (13) $ (47) Building and Construction Systems — (1) (1) (4) Extrusions (2) (4) (5) (13) Segment total (7) (21) (19) (64) Unallocated amounts: Corporate expenses — (3) — (11) Other — (3) 1 (7) Subtotal — (6) 1 (18) Other expenses, net (20) (1) (59) (2) Total $ (27) $ (28) $ (77) $ (84) (2) Effective July 1, 2020, the Company changed its inventory cost method to average cost for all U.S. inventories previously carried at LIFO cost. The effects of the change in accounting principle have been retrospectively applied to all prior periods presented in the accompanying Consolidated Financial Statements. See Note K for additional information. (3) Corporate expenses are composed of general administrative and other expenses of operating the corporate headquarters and other global administrative facilities, as well as research and development expenses of the corporate technical center. Amounts presented for all periods prior to second quarter 2020 represent an allocation of ParentCo’s corporate expenses (see Cost Allocations in Note A). (4) Metal price lag represents the financial impact of the timing difference between when aluminum prices included in Sales are recognized and when aluminum purchase prices included in Cost of goods sold are realized. This adjustment aims to remove the effect of the volatility in metal prices and the calculation of this impact considers applicable metal hedging transactions. (5) Other includes certain items that impact Cost of goods sold and Selling, general administrative, and other expenses on the Company’s Statement of Consolidated Operations that are not included in Segment Adjusted EBITDA.

Restructuring and Other Charg_2

Restructuring and Other Charges (Tables)	9 Months Ended
	Sep. 30, 2020
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Reserve by Segment	Arconic Corporation does not include Restructuring and other charges in the results of its reportable segments. The impact of allocating such charges to segment results would have been as follows: Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Rolled Products $ (1) $ 61 $ 15 $ 69 Building and Construction Systems — 2 6 31 Extrusions 1 (1) (27) (1) Segment total — 62 (6) 99 Corporate 3 2 67 5 $ 3 $ 64 $ 61 $ 104
Schedule of Restructuring Reserve	Activity and reserve balances for restructuring charges were as follows: ​ Layoff costs Other costs Total Reserve balances at December 31, 2018 $ 1 $ 3 $ 4 Cash payments (12) (3) (15) Restructuring charges 30 2 32 Other (1) 1 (1) — Reserve balances at December 31, 2019 20 1 21 Separation-related adjustments (2) 2 — 2 Cash payments (16) (2) (18) Restructuring charges 26 3 29 Other (1) (9) (1) (10) Reserve balances at September 30, 2020 (3) $ 23 $ 1 $ 24 _____________________ ​ (1) Other includes reversals of previously recorded restructuring charges and the effects of foreign currency translation.​ (2) Represents liabilities transferred from ParentCo on April 1, 2020 in connection with the Separation (see Note A).​ (3) The remaining reserves are expected to be paid in cash during the remainder of 2020, with the exception of $12 that is expected to be paid in 2021 ($11) and 2022 ($1) related to special termination benefits.​

Other Expenses (Income), Net (T

Other Expenses (Income), Net (Tables)	9 Months Ended
	Sep. 30, 2020
Other Income and Expenses [Abstract]
Schedule of Other (Income) Expense, Net	Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Non-service costs — Pension and OPEB (G) $ 20 $ 1 $ 59 $ 2 Foreign currency losses (gains), net 5 2 ​ 13 (3) Interest income — (3) ​ (4) (11) Other, net 2 — ​ 1 8 ​ $ 27 $ — ​ $ 69 $ (4)

Pension and Other Postretirem_2

Pension and Other Postretirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Schedule of Expenses Related to Pension and Other Postretirement Benefits	The following table summarizes the total expenses (excluding settlements and curtailments) recognized by Arconic Corporation related to the pension and other postretirement benefits described above: ​ ​ ​ Pension benefits Other postretirement benefits ​ ​ ​ Third quarter ended September 30, Nine months ended September 30, Third quarter ended September 30, Nine months ended September 30, Type of Plan ​ Type of Expense 2020 ​ 2019 2020 ​ 2019 2020 ​ 2019 2020 ​ 2019 Cumulative Direct Plans ​ Net periodic benefit cost $ 22 $ 1 $ 61 $ 4 $ 5 $ — $ 17 $ — Shared Plans ​ Multiemployer contribution — 16 — 46 — 4 — 15 Shared Plans ​ Cost allocation — 5 (1) 15 — 2 — 4 ​ ​ ​ $ 22 $ 22 $ 60 $ 65 $ 5 $ 6 $ 17 $ 19
Schedule of Components of Net Periodic Benefit Cost Classified as Direct Plans	The components of net periodic benefit cost for defined benefit plans classified as Cumulative Direct Plans were as follows: Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Pension benefits Service cost $ 6 $ 1 $ 16 $ 2 Interest cost 27 1 81 3 Expected return on plan assets (42) (2) (127) (4) Recognized net actuarial loss 31 1 92 3 Amortization of prior service benefit — — (1) — Settlement 3 — 58 — Net periodic benefit cost* $ 25 $ 1 $ 119 $ 4 Other postretirement benefits Service cost $ 1 $ — $ 3 $ — Interest cost 2 — 10 — Recognized net actuarial loss 3 — 6 — Amortization of prior service benefit (1) — (2) — Net periodic benefit cost* $ 5 $ — $ 17 $ — ​ __________________

Income Taxes_ (Tables)

Income Taxes​ (Tables)	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Schedule of Income Tax Provisions	The tax provisions for the third quarter of 2020 and 2019 were comprised of the following components: Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Pretax income at estimated annual effective income tax rate before discrete items $ 2 $ (5) ​ $ (5) $ 45 Impact of change in estimated annual effective tax rate on previous quarter’s pretax income 51 22 — — Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized* (48) — ​ 1 — Other discrete items 5 — ​ 9 1 Provision for income taxes $ 10 $ 17 ​ $ 5 $ 46 __________________ * The interim period impact related to operational losses in foreign jurisdictions for which no tax benefit is recognized will reverse by the end of the calendar year.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The share information used to compute basic and diluted EPS attributable to Arconic Corporation common shareholders was as follows (shares in millions): Third quarter ended September 30, Nine months ended September 30, ​ 2020 ​ 2019 2020 ​ 2019 Weighted-average shares outstanding – basic ​ 109 109 109 109 Effect of dilutive share equivalents: ​ Stock options — — — — Stock units 4 — — — Weighted-average shares outstanding – diluted 113 109 109 109

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income​ (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income	The following table details the activity of the three components that comprise Accumulated other comprehensive (loss) income for Arconic Corporation (such activity for Noncontrolling interest was immaterial for all periods presented): Third quarter ended September 30, Nine months ended September 30, 2020 ​ 2019 ​ 2020 ​ 2019 Pension and other postretirement benefits (G) ​ ​ ​ Balance at beginning of period $ (1,784) $ (32) ​ $ (43) $ (32) Establishment of additional defined benefit plans — — (1,752) — Separation-related adjustments (A) — — (50) — Other comprehensive income: ​ Unrecognized net actuarial loss and prior service benefit 4 1 ​ (34) (1) Tax (expense) benefit (1) (1) ​ 8 — Total Other comprehensive income (loss) before reclassifications, net of tax 3 — ​ (26) (1) Amortization of net actuarial loss and prior service benefit (1) 36 1 ​ 153 3 Tax expense (2) (8) — ​ (35) (1) Total amount reclassified from Accumulated other comprehensive loss, net of tax (5) 28 1 ​ 118 2 Total Other comprehensive income 31 1 ​ 92 1 Balance at end of period $ (1,753) $ (31) ​ $ (1,753) $ (31) Foreign currency translation ​ Balance at beginning of period $ (53) $ 296 ​ $ 338 $ 282 Separation-related adjustments (A) — — (396) — Other comprehensive income: Foreign currency translation (3) 37 45 20 59 Net amount reclassified to earnings from Accumulated other comprehensive income (3),(5) — — 22 — Total Other comprehensive income 37 45 ​ 42 59 Balance at end of period $ (16) $ 341 ​ $ (16) $ 341 Cash flow hedges Balance at beginning of period $ (11) $ — $ — $ — Separation-related adjustments (A) — — (4) — Other comprehensive income: Net change from periodic revaluations 2 — 4 — Tax expense (1) — (1) — Total Other comprehensive income before reclassifications, net of tax 1 — ​ 3 — Net amount reclassified to earnings (4) 14 — 3 — Tax expense (2) (3) — (1) — Total amount reclassified from Accumulated other comprehensive loss, net of tax (5) 11 — ​ 2 — Total Other comprehensive income 12 — ​ 5 — Balance at end of period $ 1 $ — ​ $ 1 $ — Accumulated other comprehensive (loss) income $ (1,768) $ 310 ​ $ (1,768) $ 310 _____________________ (1) These amounts were included in the non-service component of net periodic benefit cost for pension and other postretirement benefits (see Note G). In the 2020 third quarter and nine-month period, these amounts include $3 and $58 related to the settlement of certain pension benefits (see Note G). (2) These amounts were reported 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. In the 2020 nine-month period, the net amount reclassified to earnings was reported in Restructuring and other charges on the accompanying Statement of Consolidated Operations related to the sale of certain foreign subsidiaries. (4) These amounts relate to aluminum contracts, a portion of which were reported in both Sales and Cost of goods sold 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. These amounts were reflected on the accompanying Statement of Consolidated Operations in the line items indicated in footnotes 1 through 4.

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Inventory Disclosure [Abstract]
Schedule of Inventories	​ September 30, 2020 ​ December 31, 2019 Finished goods $ 242 $ 237 Work-in-process 525 746 Purchased raw materials 66 85 Operating supplies 68 69 ​ $ 901 $ 1,137
Accounting Standards Update and Change in Accounting Principle	The following table compares the amounts that were reported under average cost in the Consolidated Financial Statements as of and for the quarter and nine months ended September 30, 2020 with the amounts had they continued to be reported under LIFO: As Reported under As Computed under LIFO Effect of Change Statement of Consolidated Operations for the third quarter ended September 30, 2020: Cost of goods sold $ 1,218 $ 1,232 $ (14) Operating income 64 50 14 Income before income taxes 15 1 14 Provision for income taxes 10 6 4 Net income (loss) 5 (5) 10 Net income (loss) attributable to Arconic Corporation 5 (5) 10 Earnings per share attributable to Arconic Corporation common shareholders: Basic $ 0.05 $ (0.05) $ 0.10 Diluted 0.05 (0.05) 0.10 Statement of Consolidated Operations for the nine months ended September 30, 2020: Cost of goods sold $ 3,614 $ 3,605 $ 9 Operating income 126 135 (9) Loss before income taxes (40) (31) (9) Provision for income taxes 5 6 (1) As Reported under As Computed under LIFO Effect of Change Net loss (45) (37) (8) Net loss attributable to Arconic Corporation (45) (37) (8) Earnings per share attributable to Arconic Corporation common shareholders: Basic $ (0.41) $ (0.34) $ (0.07) Diluted (0.41) (0.34) (0.07) Statement of Consolidated Comprehensive Income for the third quarter ended September 30, 2020: Comprehensive income $ 85 $ 75 $ 10 Comprehensive income attributable to Arconic Corporation 85 75 10 Statement of Consolidated Comprehensive Income for the nine months ended September 30, 2020: Comprehensive income $ 94 $ 102 $ (8) Comprehensive income attributable to Arconic Corporation 94 102 (8) Consolidated Balance Sheet as of September 30, 2020: Inventories $ 901 $ 591 $ 310 Deferred income tax assets 296 366 (70) Additional capital 3,332 3,098 234 Accumulated deficit (91) (97) 6 Statement of Consolidated Cash Flows for the nine months ended September 30, 2020: Net loss $ (45) $ (37) $ (8) Deferred income taxes 28 29 (1) Decrease in inventories 197 188 9	Additionally, certain financial statement line items in the accompanying Consolidated Balance Sheet as of December 31, 2019 and each of the Statement of Consolidated Operations, Statement of Consolidated Comprehensive Income, and Statement of Consolidated Cash Flows for the 2019 third quarter and nine-month period were recast as follows: As Previously Reported Effect of Change As Recast Statement of Consolidated Operations for the third quarter ended September 30, 2019: Cost of goods sold $ 1,543 $ 22 $ 1,565 Operating income 44 (22) 22 Income (loss) before income taxes 15 (22) (7) Provision for income taxes 22 (5) 17 Net loss (7) (17) (24) Net loss attributable to Arconic Corporation (7) (17) (24) Earnings per share attributable to Arconic Corporation common shareholders: Basic $ (0.07) $ (0.15) $ (0.22) Diluted (0.07) (0.15) (0.22) Statement of Consolidated Operations for the nine months ended September 30, 2019: Cost of goods sold $ 4,810 $ 39 $ 4,849 Operating income 176 (39) 137 Income before income taxes 94 (39) 55 Provision for income taxes 55 (9) 46 Net income 39 (30) 9 Net income attributable to Arconic Corporation 39 (30) 9 Earnings per share attributable to Arconic Corporation common shareholders: Basic $ 0.35 $ (0.27) $ 0.08 Diluted 0.35 (0.27) 0.08 As Previously Reported Effect of Change As Recast Statement of Consolidated Comprehensive Income for the third quarter ended September 30, 2019: Comprehensive income $ 39 $ (17) $ 22 Comprehensive income attributable to Arconic Corporation 39 (17) 22 Statement of Consolidated Comprehensive Income for the nine months ended September 30, 2019: Comprehensive income $ 99 $ (30) $ 69 Comprehensive income attributable to Arconic Corporation 99 (30) 69 Consolidated Balance Sheet as of December 31, 2019: Inventories $ 820 $ 317 $ 1,137 Deferred income tax liabilities 87 72 159 Parent Company net investment 2,419 245 2,664 Statement of Consolidated Cash Flows for the nine months ended September 30, 2019: Net income $ 39 $ (30) $ 9 Deferred income taxes 20 (9) 11 (Increase) in inventories (69) 39 (30)

Leases_ (Tables)

Leases​ (Tables)	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Schedule of Operating Lease Maturity	Future minimum contractual operating lease obligations were as follows: ​ September 30, 2020 ​ December 31, 2019 2020 $ 11 $ 38 2021 38 29 2022 31 22 2023 24 17 2024 19 14 Thereafter 53 38 Total lease payments $ 176 $ 158 Less: imputed interest 33 29 Present value of lease liabilities $ 143 $ 129

The Separation and Basis of P_3

The Separation and Basis of Presentation - Narrative (Details) $ / shares in Units, $ in Millions	Apr. 01, 2020USD ($)$ / sharesshares	Sep. 30, 2020USD ($)employee	Mar. 31, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 01, 2020USD ($)	Jun. 30, 2020USD ($)	Sep. 30, 2020USD ($)employee	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Feb. 05, 2020	Jan. 02, 2020USD ($)	Feb. 08, 2019company
Related Party Transaction [Line Items]
Reduction of planned capital expenditures					$ 50
Reduction of planned capital expenditures, percentage					30.00%
Number of publicly traded companies | company												2
Separation transaction, share conversion ratio										0.25
Separation transaction, payment to parent	$ 728
Separation transaction, shares issued to parent | shares	109,021,376
Common stock, par value (in dollars per share) | $ / shares	$ 0.01
Separation transaction, costs incurred				$ 13			$ 18	$ 23
Receivables from customers		$ 629					629		$ 384		$ 281
Accounts payable, settlement arrangements									1
Restructuring and other charges		$ 3		64			$ 61	104
Number of employees separated | employee		30					440
(Decrease) in accounts payable, trade (A)							$ (165)	(96)
Capital expenditures (A)							(126)	(120)
Previously Reported [Member]
Related Party Transaction [Line Items]
(Decrease) in accounts payable, trade (A)			$ 35			$ 43
Capital expenditures (A)			$ (35)			$ (43)
Spin-off
Related Party Transaction [Line Items]
Restructuring and other charges		$ 0		2			2	5
ParentCo | Sale of customer receivables
Related Party Transaction [Line Items]
Transaction with related party, amount									$ 281
ParentCo
Related Party Transaction [Line Items]
Third-party sales-related party		24		41			81	142
Accounts Receivable, Related Parties		$ 13					13
ParentCo
Related Party Transaction [Line Items]
Separation transaction, costs incurred				$ 25			$ 38	$ 44
Common stock, outstanding (in shares) | shares	436,085,504
Revenue | Product | Ground Transportation
Related Party Transaction [Line Items]
Concentration risk, percentage								35.00%
Revenue | Product | Aerospace
Related Party Transaction [Line Items]
Concentration risk, percentage								18.00%
Revenue | Customer | Ford | Aerospace
Related Party Transaction [Line Items]
Concentration risk, percentage								13.00%
Board of Directors
Related Party Transaction [Line Items]
Salary reduction, percentage					30.00%
CEO
Related Party Transaction [Line Items]
Salary reduction, percentage					30.00%
Senior-level management
Related Party Transaction [Line Items]
Salary reduction, percentage					20.00%
Salaried employees
Related Party Transaction [Line Items]
Salary reduction, percentage					10.00%
Salaried workforce
Related Party Transaction [Line Items]
Salary reduction, percentage					10.00%

The Separation and Basis of P_4

The Separation and Basis of Presentation - Cost Allocations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Restructuring Cost and Reserve [Line Items]
Cost of goods sold	$ 1,218	$ 1,565	$ 3,614	$ 4,849
Selling, general administrative, and other expenses	59	82	194	255
Research and development expenses	8	9	27	34
Provision for depreciation and amortization	63	63	191	190
Restructuring and other charges	3	64	61	104
Interest expense	22	29	97	86
Other expenses (income), net (F)	27	0	69	(4)
Separation transaction, costs incurred		13	18	23
Spin-off
Restructuring Cost and Reserve [Line Items]
Cost of goods sold	0	4	0	11
Selling, general administrative, and other expenses	0	27	25	80
Research and development expenses	0	1	0	8
Provision for depreciation and amortization	0	4	1	9
Restructuring and other charges	0	2	2	5
Interest expense	0	29	28	86
Other expenses (income), net (F)	$ 0	$ 1	$ (5)	$ 4

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	$ 1,415	$ 1,805	$ 4,213	$ 5,569
Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	1,419	1,810	4,232	5,590
Ground Transportation
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	518	618	1,304	1,966
Building and Construction
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	283	329	837	1,004
Aerospace
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	151	311	688	975
Industrial Products and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	265	311	817	937
Packaging
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	198	236	571	687
Products and Services, Net | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	1,415	1,805	4,217	5,569
Rolled Products [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	1,092	1,397	3,194	4,294
Rolled Products [Member] | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	1,095	1,401	3,208	4,314
Rolled Products [Member] | Ground Transportation
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	493	592	1,242	1,878
Rolled Products [Member] | Building and Construction
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	42	47	110	149
Rolled Products [Member] | Aerospace
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	107	243	505	754
Rolled Products [Member] | Industrial Products and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	252	279	766	826
Rolled Products [Member] | Packaging
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	198	236	571	687
Extrusions [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	82	126	296	420
Extrusions [Member] | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	83	127	297	421
Extrusions [Member] | Ground Transportation
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	25	26	62	88
Extrusions [Member] | Building and Construction
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	0	0	0	0
Extrusions [Member] | Aerospace
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	44	68	183	221
Extrusions [Member] | Industrial Products and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	13	32	51	111
Extrusions [Member] | Packaging
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	0	0	0	0
Building and Construction Systems [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	241	282	727	855
Building and Construction Systems [Member] | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	241	282	727	855
Building and Construction Systems [Member] | Ground Transportation
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	0	0	0	0
Building and Construction Systems [Member] | Building and Construction
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	241	282	727	855
Building and Construction Systems [Member] | Aerospace
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	0	0	0	0
Building and Construction Systems [Member] | Industrial Products and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	0	0	0	0
Building and Construction Systems [Member] | Packaging
Segment Reporting, Revenue Reconciling Item [Line Items]
Total end-market revenue	$ 0	$ 0	$ 0	$ 0

Segment and Related Informati_3

Segment and Related Information​ - Operating Results (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	$ 1,415	$ 1,805	$ 4,213	$ 5,569
Segment Adjusted EBITDA	(172)	(191)	(483)	(589)
Provision for depreciation and amortization	63	63	191	190
Restructuring and other charges	3	64	61	104
Net Income (Loss) Attributable to Parent	5	(24)	(45)	9
Rolled Products [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	1,092	1,397	3,194	4,294
Segment Adjusted EBITDA	(138)	(160)	(388)	(499)
Provision for depreciation and amortization	48	46	147	139
Restructuring and other charges	1	61	15	69
Extrusions [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	82	126	296	420
Segment Adjusted EBITDA	(6)	(8)	(12)	(6)
Provision for depreciation and amortization	6	7	18	22
Restructuring and other charges	1	1	27	1
Building and Construction Systems [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	241	282	727	855
Segment Adjusted EBITDA	(40)	(39)	(107)	(96)
Provision for depreciation and amortization	5	4	14	14
Restructuring and other charges	0	2	6	31
Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	1,419	1,810	4,232	5,590
Segment Adjusted EBITDA	(172)	(191)	(483)	(589)
Provision for depreciation and amortization	59	57	179	175
Restructuring and other charges	0	62	6	99
Operating segments | Rolled Products [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	1,095	1,401	3,208	4,314
Operating segments | Extrusions [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	83	127	297	421
Operating segments | Building and Construction Systems [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	241	282	727	855
Intersegment sales
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	4	5	15	21
Intersegment sales | Rolled Products [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	3	4	14	20
Intersegment sales | Extrusions [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	1	1	1	1
Intersegment sales | Building and Construction Systems [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	0	0	0	0
Sales to unrelated parties
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	1,391	1,764	4,132	5,427
Sales to unrelated parties | Rolled Products [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	1,073	1,366	3,144	4,193
Sales to unrelated parties | Extrusions [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	77	116	265	379
Sales to unrelated parties | Building and Construction Systems [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	241	282	727	855
Sales to unrelated parties | Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	1,391	1,764	4,136	5,427
Sales to related parties
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	24	41	81	142
Sales to related parties | Rolled Products [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	19	31	50	101
Sales to related parties | Extrusions [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	5	10	31	41
Sales to related parties | Building and Construction Systems [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	0	0	0	0
Sales to related parties | Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Sales	$ 24	$ 41	$ 81	$ 142

Segment and Related Informati_4

Segment and Related Information​ - Segment Operating Profit (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Segment Adjusted EBITDA	$ 172	$ 191	$ 483	$ 589
Stock-based compensation expense	(6)	(10)	(18)	(28)
Metal Price Lag	(16)	(10)	(30)	(33)
Provision for depreciation and amortization	(63)	(63)	(191)	(190)
Restructuring and other charges	(3)	(64)	(61)	(104)
Other	(14)	(12)	(42)	(54)
Operating Income (Loss)	64	22	126	137
Interest expense	(22)	(29)	(97)	(86)
Other (expenses) income, net	(27)	0	(69)	4
Provision for income taxes (H)	(10)	(17)	(5)	(46)
Net Income (Loss) Attributable to Noncontrolling Interest	0	0	0	0
Income before income taxes	15	(7)	(40)	55
Non-service costs — Pension and OPEB (G)	27	28	77	84
Net Income (Loss) Attributable to Parent	5	(24)	(45)	9
Non-service costs — Pension and OPEB (G)	(20)	(1)	(59)	(2)
Rolled Products [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Segment Adjusted EBITDA	138	160	388	499
Provision for depreciation and amortization	(48)	(46)	(147)	(139)
Restructuring and other charges	(1)	(61)	(15)	(69)
Non-service costs — Pension and OPEB (G)	5	16	13	47
Extrusions [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Segment Adjusted EBITDA	6	8	12	6
Provision for depreciation and amortization	(6)	(7)	(18)	(22)
Restructuring and other charges	(1)	(1)	(27)	(1)
Non-service costs — Pension and OPEB (G)	2	4	5	13
Building and Construction Systems [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Segment Adjusted EBITDA	40	39	107	96
Provision for depreciation and amortization	(5)	(4)	(14)	(14)
Restructuring and other charges	0	(2)	(6)	(31)
Non-service costs — Pension and OPEB (G)	0	1	1	4
Other Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Non-service costs — Pension and OPEB (G)	0	3	(1)	7
Corporate Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Corporate Expenses	(6)	(10)	(15)	(43)
Restructuring and other charges	(3)	(2)	(67)	(5)
Non-service costs — Pension and OPEB (G)	0	3	0	11
Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Segment Adjusted EBITDA	172	191	483	589
Provision for depreciation and amortization	(59)	(57)	(179)	(175)
Restructuring and other charges	0	(62)	(6)	(99)
Non-service costs — Pension and OPEB (G)	7	21	19	64
Segment Reconciling Items [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Non-service costs — Pension and OPEB (G)	$ 0	$ 6	$ (1)	$ 18

Restructuring and Other Charg_3

Restructuring and Other Charges - Restructuring Reserve (Details) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)employee	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)employeeclaimants	Sep. 30, 2019USD ($)	Dec. 31, 2022USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2019USD ($)
Restructuring Reserve [Roll Forward]
Beginning balance				$ 21	$ 4			$ 4
Cash payments				(18)				(15)
Restructuring charges				29				32
Other				(10)				0
Ending balance		$ 24		24				21
Restructuring and other charges		(3)	$ (64)	(61)	(104)
Separation-related adjustments (A)		8		324
Restructuring and other charges (E)		$ 3	64	$ 61	104
Number of employees separated | employee		30		440
Forecast
Restructuring Reserve [Roll Forward]
Cash payments	$ (12)					$ (1)	$ (11)
Hard Alloy Extrusions Plant in South Korea
Restructuring Reserve [Roll Forward]
Gain (Loss) on Disposition of Business				$ 25
Aluminum Rolling Mill in Brazil
Restructuring Reserve [Roll Forward]
Restructuring and other charges			(59)		(59)
Gain (Loss) on Disposition of Business				25
Operating segments
Restructuring Reserve [Roll Forward]
Restructuring and other charges		$ 0	(62)	(6)	(99)
Rolled Products [Member]
Restructuring Reserve [Roll Forward]
Restructuring and other charges		(1)	(61)	(15)	(69)
Building and Construction Systems [Member]
Restructuring Reserve [Roll Forward]
Restructuring and other charges		0	(2)	(6)	(31)
Extrusions [Member]
Restructuring Reserve [Roll Forward]
Restructuring and other charges		(1)	(1)	(27)	(1)
Corporate Segment
Restructuring Reserve [Roll Forward]
Restructuring and other charges		(3)	(2)	(67)	(5)
Layoff costs
Restructuring Reserve [Roll Forward]
Beginning balance				20	1			1
Cash payments				(16)				(12)
Restructuring charges				26				30
Other				(9)				1
Ending balance		23		23				20
Restructuring and other charges		(1)		(18)
Separation-related adjustments (A)				2
Layoff costs | Building and Construction System and Extrustions [Member]
Restructuring Reserve [Roll Forward]
Restructuring and other charges				$ (8)
Number of employees separated | claimants				140
Other costs
Restructuring Reserve [Roll Forward]
Beginning balance				$ 1	3			3
Cash payments				(2)				(3)
Restructuring charges				3				2
Other				(1)				(1)
Ending balance		1		1				$ 1
Restructuring and other charges		(1)		(7)	(2)
Separation-related adjustments (A)				0
Other costs | Building and Construction System and Extrustions [Member]
Restructuring Reserve [Roll Forward]
Restructuring and other charges				(11)
Spin-off
Restructuring Reserve [Roll Forward]
Restructuring and other charges		$ 0	$ (2)	(2)	$ (5)
Separation-related adjustments (A)				$ 2

Restructuring and Other Charg_4

Restructuring and Other Charges - Narrative (Details) $ in Millions	Mar. 01, 2020USD ($)	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)employee	Jun. 30, 2020USD ($)	Sep. 30, 2019USD ($)employee	Sep. 30, 2020USD ($)employeeclaimants	Sep. 30, 2019USD ($)employee	Dec. 31, 2022USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2019USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)			$ 3		$ 64	$ 61	$ 104
Restructuring and other charges			$ 3		64	$ 61	104
Number of employees separated | employee			30			440
Cash payments, restructuring						$ 18				$ 15
Forecast
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring		$ 12						$ 1	$ 11
2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Expected number of employees separated | employee						580
Number of employees separated | employee						310
2019 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Expected number of employees separated | employee						370
Number of employees separated | employee						340
2019 Restructuring Program [Member] | Previously Reported [Member]
Restructuring Cost and Reserve [Line Items]
Expected number of employees separated | employee						480
Layoff costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 1			$ 18
Cash payments, restructuring						16				12
Layoff costs | 2020 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring			3			8
Layoff costs | 2019 Restructuring Program [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring			2			8
Allocated costs, ParentCo
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			0		2	2	5
Other miscellaneous costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			1			7	2
Cash payments, restructuring						2				$ 3
Pension Settlement Cost [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			3			58
Reversal of Reserve [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 2			14
Environmental [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges						5
Legacy Non-Income Taxes [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges						4
Impairment of Carrying Value of Tradename [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges							10
Hard Alloy Extrusions Plant in South Korea | Disposed of by sale
Restructuring Cost and Reserve [Line Items]
Gain (loss) on sale	$ 31			$ 1
Aluminum Rolling Mill in Brazil
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 59		$ 59
Rolled Products and Building and Construction Systems
Restructuring Cost and Reserve [Line Items]
Number of employees separated | employee					120		370
Rolled Products and Building and Construction Systems | Layoff costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 3		$ 28
Building and Construction System and Extrustions [Member] | Layoff costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges						$ 8
Number of employees separated | claimants						140
Building and Construction System and Extrustions [Member] | Other miscellaneous costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges						$ 11

Other Expenses (Income), Net (D

Other Expenses (Income), Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Income and Expenses [Abstract]
Interest income	$ 0	$ (3)	$ (4)	$ (11)
Foreign currency losses (gains), net	5	2	13	(3)
Non-service costs — Pension and OPEB (G)	20	1	59	2
Other, net	2	0	1	8
Other (income) expenses, net	27	0	69	(4)
Segment Adjusted EBITDA	172	191	483	589
Restructuring and other charges	(3)	(64)	(61)	(104)
Other	(14)	(12)	(42)	(54)
Operating Income (Loss)	$ 64	$ 22	$ 126	$ 137

Pension and Other Postretirem_3

Pension and Other Postretirement Benefits - Narrative (Details) $ in Millions	Jan. 01, 2020USD ($)	Jun. 30, 2020USD ($)	Sep. 30, 2020USD ($)participants	Jun. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)participants	Sep. 30, 2020USD ($)participants	Sep. 30, 2019USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Jul. 31, 2020	Jun. 01, 2020participants	Apr. 01, 2020USD ($)	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Retirement plans, liability	$ 1,920
Retirement plans, current liability	60
Retirement plans, benefit obligation	4,255
Retirement plans, plan assets	2,335
Establishment of retirement plans, AOCI	$ 1,752					$ 50
Expected employer contributions, 2020			$ 280			280	$ 280
Liability, Defined Benefit Plan, Noncurrent													$ 15
asset, defined benefit plan													$ 65
Liability, Other Postretirement Defined Benefit Plan			7			7	7
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax			5
U.K. Defined Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement							250
Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost										$ 100
Service cost										$ 25
Payment for Pension and Other Postretirement Benefits									$ 20
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost			25		$ 1		119	$ 4
Service cost			6		1		16	2
Multiemployer contribution expense			0		16		0	46
Expected employer contributions, 2020			260			260	260
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		1.55%		1.55%										2.05%
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost			5		0		17	0
Service cost			1		0		3	0
Multiemployer contribution expense			0		$ 4		0	$ 15
Expected employer contributions, 2020			55			55	55
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate											2.54%			3.17%
Other Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions, 2020			10			10	10
U.K. Defined Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Retirement plans, benefit obligation			240			240	240
Retirement plans, plan assets			$ 260			$ 260	$ 260
Defined Benefit Plan, Participants | participants			1,050			1,050	1,050					1,800
Defined Benefit Plan, Plan Assets, Contributions by Employer				$ 10
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement			$ 3				$ 58
U.K. Defined Benefit Plan [Member] | ParentCo
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Participants | participants												3,350
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement		$ 400
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Assets Transferred to (from) Plan		$ 460

Pension and Other Postretirem_4

Pension and Other Postretirement Benefits - Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 25	$ 1	$ 119	$ 4
Multiemployer contribution	0	16	0	46
Cost allocation	0	(5)	(1)	(15)
Pension and other postretirement benefits cost	22	22	60	65
Pension benefits | Cumulative Direct Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	22	1	61	4
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	5	0	17	0
Multiemployer contribution	0	4	0	15
Cost allocation	0	(2)	0	(4)
Pension and other postretirement benefits cost	5	6	17	19
Other postretirement benefits | Cumulative Direct Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 5	$ 0	$ 17	$ 0

Pension and Other Postretirem_5

Pension and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 6	$ 1	$ 16	$ 2
Interest cost	27	1	81	3
Expected return on plan assets	(42)	(2)	(127)	(4)
Settlement	31	1	92	3
Amortization of prior service benefit	0	0	(1)	0
Net periodic benefit cost	25	1	119	4
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	3	0	58	0
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1	0	3	0
Interest cost	2	0	10	0
Settlement	3	0	6	0
Amortization of prior service benefit	(1)	0	(2)	0
Net periodic benefit cost	$ 5	$ 0	$ 17	$ 0

Income Taxes_ (Details)

Income Taxes​ (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)points	Sep. 30, 2019USD ($)points
Income Tax Disclosure [Abstract]
Effective income tax rate, including discrete items	66.70%	(242.90%)	11.70%	80.00%
Effective Income Tax Rate Reconciliation, Percentage Points | points			9.3	59
Income Tax Expense (Benefit)
Provision for depreciation and amortization	$ 2	$ (5)	$ (5)	$ 45
Impact of change in estimated annual effective tax rate on previous quarter’s pretax income	51	22	0	0
Interim period treatment of operational losses in foreign jurisdictions for which no tax benefit is recognized*	$ (48)	$ 0	$ 1	$ 0
Other discrete items	5	0	9	1
Provision for income taxes (H)	$ 10	$ 17	$ 5	$ 46

Earnings Per Share (Details)

Earnings Per Share (Details) - $ / shares	Apr. 01, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted Average Number of Shares Outstanding, Basic	109,021,376	109,000,000	109,000,000	109,000,000	109,000,000
Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends		4,000,000
Weighted Average Number of Shares Outstanding, Diluted		113,000,000	109,000,000	109,000,000	109,000,000
Equity Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount				1,000,000
Weighted Average Exercise Price Of Underwater Options				$ 27.97
Stock Awards and Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares That Would Have Been Included In Diluted Earnings Per Share Calculation				$ 2,000,000

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income​ (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Apr. 01, 2020
AOCI Attributable to Parent [Abstract]
Balance at beginning of period	$ 1,389	$ 3,117	$ 2,973	$ 2,969
Separation-related adjustments (A)	(8)		(324)
Other comprehensive income:
Foreign currency translation	37	45	42	59
Total Other comprehensive income, net of tax	80	46	139	60
Balance at end of period	1,488	3,003	1,488	3,003
U.K. Defined Benefit Plan [Member]
Other comprehensive income:
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement	3		58
Pension and other postretirement benefits
AOCI Attributable to Parent [Abstract]
Balance at beginning of period	(1,784)	(32)	(43)	(32)
Establishment of additional defined benefit plans					$ (1,752)
Separation-related adjustments (A)	0	0	50	0
Other comprehensive income:
Other Comprehensive Income (Loss), before Reclassifications, before Tax	4	1	(34)	(1)
Other Comprehensive Income (Loss) before Reclassifications, Tax	(1)	(1)	8	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	3	0	(26)	(1)
Amortization of net actuarial loss and prior service cost	36	1	153	3
Tax expense	(8)	0	(35)	(1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	28	1	118	2
Total Other comprehensive income, net of tax	31	1	92	1
Balance at end of period	(1,753)	(31)	(1,753)	(31)
Foreign currency translation
AOCI Attributable to Parent [Abstract]
Balance at beginning of period	(53)	296	338	282
Separation-related adjustments (A)	0	0	396	0
Other comprehensive income:
Foreign currency translation	37	45	20	59
Net amount reclassified to earnings from Accumulated other comprehensive income	0	0	22	0
Total Other comprehensive income, net of tax	37	45	42	59
Balance at end of period	(16)	341	(16)	341
Cash flow hedges
AOCI Attributable to Parent [Abstract]
Balance at beginning of period	(11)	0	0	0
Separation-related adjustments (A)	0	0	(4)	0
Other comprehensive income:
Other Comprehensive Income (Loss), before Reclassifications, before Tax	2	0	4	0
Other Comprehensive Income (Loss) before Reclassifications, Tax	(1)	0	(1)	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	1	0	3	0
Amortization of net actuarial loss and prior service cost	14	0	3	0
Tax expense	(3)	0	(1)	0
Total amount reclassified from Accumulated other comprehensive loss, net of tax	11	0	2	0
Total Other comprehensive income, net of tax	12	0	5	0
Balance at end of period	1	0	1	0
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent [Abstract]
Balance at beginning of period	(1,848)	264	295	250
Separation-related adjustments (A)			(450)
Other comprehensive income:
Total Other comprehensive income, net of tax	80	46	139	60
Balance at end of period	$ (1,768)	$ 310	$ (1,768)	$ 310

Inventories (Details)

Inventories (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 01, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Inventory [Line Items]
Separation-related adjustments (A)		$ 8		$ 324
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		85	$ 22	94	$ 69
Inventories (K)		901		901		$ 1,137
Deferred income taxes		12		12		159
Parent Company net investment (A)		0		0		2,664
Net income (loss)		5	(24)	(45)	9
Deferred income taxes				28	11
Decrease (Increase) in inventories				197	(30)
Cost of goods sold (exclusive of expenses below) (K)		1,218	1,565	3,614	4,849
Operating Income (Loss)		64	22	126	137
Income before income taxes		15	(7)	(40)	55
Provision for income taxes (H)		10	17	5	46
Net Income (Loss) Attributable to Parent		$ 5	$ (24)	$ (45)	$ 9
Basic (in dollars per share)		$ 0.05	$ (0.22)	$ (0.41)	$ 0.08
Diluted (in dollars per share)		$ 0.05	$ (0.22)	$ (0.41)	$ 0.08
Deferred income taxes		$ 296		$ 296		14
Additional capital		3,332		3,332		0
Accumulated deficit		(91)		(91)		0
Finished goods		242		242		237
Work-in-process		525		525		746
Purchased raw materials		66		66		85
Operating supplies		68		68		69
Inventory, gross		901		901		1,137
Previously Reported [Member]
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest			$ 39		$ 99
Inventories (K)						820
Deferred income taxes						87
Parent Company net investment (A)						2,419
Net income (loss)			(7)		39
Deferred income taxes					20
Decrease (Increase) in inventories					(69)
Cost of goods sold (exclusive of expenses below) (K)			1,543		4,810
Operating Income (Loss)			44		176
Income before income taxes			15		94
Provision for income taxes (H)			22		55
Net Income (Loss) Attributable to Parent			$ (7)		$ 39
Basic (in dollars per share)			$ (0.07)		$ 0.35
Diluted (in dollars per share)			$ (0.07)		$ 0.35
Revision of Prior Period, Change in Accounting Principle, Adjustment
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest			$ (17)		$ (30)
Inventories (K)						317
Deferred income taxes						72
Parent Company net investment (A)						$ 245
Net income (loss)			(17)		(30)
Deferred income taxes					(9)
Decrease (Increase) in inventories					39
Cost of goods sold (exclusive of expenses below) (K)			22		39
Operating Income (Loss)			(22)		(39)
Income before income taxes			(22)		(39)
Provision for income taxes (H)			(5)		(9)
Net Income (Loss) Attributable to Parent			$ (17)		$ (30)
Basic (in dollars per share)			$ (0.15)		$ (0.27)
Diluted (in dollars per share)			$ (0.15)		$ (0.27)
Change in Accounting Principle, Other
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		75		102
Inventories (K)		591		591
Net income (loss)		(5)		(37)
Deferred income taxes				29
Decrease (Increase) in inventories				188
Cost of goods sold (exclusive of expenses below) (K)		1,232		3,605
Operating Income (Loss)		50		135
Income before income taxes		1		(31)
Provision for income taxes (H)		6		6
Net Income (Loss) Attributable to Parent		$ (5)		$ (37)
Basic (in dollars per share)		$ (0.05)		$ (0.34)
Diluted (in dollars per share)		$ (0.05)		$ (0.34)
Deferred income taxes		$ 366		$ 366
Additional capital		3,098		3,098
Accumulated deficit		(97)		(97)
Change In Accounting Principle, Adjustment
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		10		(8)
Inventories (K)		310		310
Net income (loss)		10		(8)
Deferred income taxes				(1)
Decrease (Increase) in inventories				9
Cost of goods sold (exclusive of expenses below) (K)		(14)		9
Operating Income (Loss)		14		(9)
Income before income taxes		14		(9)
Provision for income taxes (H)		4		(1)
Net Income (Loss) Attributable to Parent		$ 10		$ (8)
Basic (in dollars per share)		$ 0.10		$ (0.07)
Diluted (in dollars per share)		$ 0.10		$ (0.07)
Deferred income taxes		$ (70)		$ (70)
Additional capital		234		234
Accumulated deficit		6		6
Parent Company net investment
Inventory [Line Items]
Separation-related adjustments (A)				2,548
Net income (loss)		0	$ (24)	46	$ 9
Parent Company net investment | Revision of Prior Period, Change in Accounting Principle, Adjustment
Inventory [Line Items]
Separation-related adjustments (A)	$ 293
Arconic Corporation
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		85	22	94	69
Net income (loss)		5	(24)	(45)	9
Arconic Corporation | Previously Reported [Member]
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest			39		99
Arconic Corporation | Revision of Prior Period, Change in Accounting Principle, Adjustment
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest			$ (17)		$ (30)
Arconic Corporation | Change in Accounting Principle, Other
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		75		102
Arconic Corporation | Change In Accounting Principle, Adjustment
Inventory [Line Items]
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		$ 10		$ (8)

Leases_ (Details)

Leases​ (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Leases [Abstract]
Lease cost	$ 14	$ 15	$ 43	$ 47
Right-of-use asset obtained in exchange for operating lease liability	$ 6		$ 38
Weighted-average remaining lease term	6 years 8 months 12 days		6 years 8 months 12 days		6 years 8 months 12 days
Weighted-average discount rate	5.90%		5.90%		6.00%
Operating Lease Obligation
2020	$ 11		$ 11		$ 38
2021	38		38		29
2022	31		31		22
2023	24		24		17
2024	19		19		14
Thereafter	53		53		38
Total lease payments	176		176		158
Less: imputed interest	33		33		29
Present value of lease liabilities	$ 143		$ 143		$ 129

Debt 144A due 2028 and Credit A

Debt 144A due 2028 and Credit Agreement (Details) - USD ($)	May 13, 2020	Apr. 02, 2020	Apr. 01, 2020	Mar. 25, 2020	Feb. 07, 2020	Feb. 05, 2020	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020	Aug. 01, 2012
Debt Instrument [Line Items]
Debt instrument, face amount						$ 1,200,000,000
Proceeds from debt issuance						$ 1,168,000,000	$ 2,400,000,000	$ 0
Cash			$ 500,000,000						$ 60,000,000
Separation payment to former parent company (A)			$ 728,000,000				728,000,000
Senior Secured Notes | Second-Lien Notes due 2028, 6.125%
Debt Instrument [Line Items]
Debt instrument, face amount					$ 600,000,000
Fixed interest rate					6.125%
Proceeds from debt issuance					$ 593,000,000
Debt, carrying value							1,277,000,000
Senior Secured Notes | First-Lien Notes due 2025, 6.000%
Debt Instrument [Line Items]
Debt instrument, face amount	$ 700,000,000
Fixed interest rate	6.00%
Proceeds from debt issuance	$ 691,000,000
Debt Issuance Costs, Net							15,000,000
Unamortized Debt Issuance Expense							12,000,000
Interest Expense, Other Long-term Debt							19,000,000
Write off of Deferred Debt Issuance Cost							3,000,000
Debt, carrying value							1,365,000,000
Senior Secured Loans | First-Lien Term B Loan Facility
Debt Instrument [Line Items]
Debt instrument, face amount	600,000,000			$ 600,000,000
Debt instrument, term				7 years
Proceeds from debt issuance				$ 575,000,000
Debt Issuance Costs, Net							30,000,000
Unamortized Debt Issuance Expense							14,000,000
Interest Expense, Other Long-term Debt							19,000,000
Write off of Deferred Debt Issuance Cost							16,000,000
Senior Secured Credit Facility | First-Lien Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, face amount				$ 1,000
Debt instrument, term				5 years
Basis spread on variable rate		2.00%
Proceeds from revolving credit facility	$ 500,000,000	$ 500,000,000
Debt Issuance Costs, Net							30,000,000
Unamortized Debt Issuance Expense							14,000,000
Interest Expense, Other Long-term Debt							19,000,000
Write off of Deferred Debt Issuance Cost							16,000,000
Senior Secured Credit Facility | ABL Credit Agreement | Revolving Credit Facility | Deutsche Bank AG New York Branch
Debt Instrument [Line Items]
Debt Issuance Costs, Net							15,000,000
Unamortized Debt Issuance Expense							12,000,000
Interest Expense, Other Long-term Debt							19,000,000
Write off of Deferred Debt Issuance Cost							3,000,000
Revolving credit facility, current borrowing capacity							681,000,000
Required fixed charge coverage ratio	1
Senior Secured Credit Facility | ABL Credit Agreement | Revolving Credit Facility | LIBOR | Deutsche Bank AG New York Branch
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Bonds [Member] | Midwestern Disaster Area Revenue Bonds Series 2012 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount										$ 250,000,000
Secured Debt and Line of Credit [Member] | First-Lien Revolving Credit Facility and Second-Lien Notes due 2028, 6.125% [Member]
Debt Instrument [Line Items]
Debt Issuance Costs, Net							$ 42,000,000
Minimum | Senior Secured Notes | Second-Lien Notes due 2028, 6.125%
Debt Instrument [Line Items]
Required prior notice for debt redemption, term					10 days
Minimum | Senior Secured Notes | First-Lien Notes due 2025, 6.000%
Debt Instrument [Line Items]
Required prior notice for debt redemption, term	10 days
Minimum | Senior Secured Credit Facility | ABL Credit Agreement | Revolving Credit Facility | LIBOR | Deutsche Bank AG New York Branch
Debt Instrument [Line Items]
Fixed interest rate	0.75%
Maximum | Senior Secured Notes | Second-Lien Notes due 2028, 6.125%
Debt Instrument [Line Items]
Required prior notice for debt redemption, term					60 days
Maximum | Senior Secured Notes | First-Lien Notes due 2025, 6.000%
Debt Instrument [Line Items]
Required prior notice for debt redemption, term	60 days
Redemption prior to February 15, 2023 | Senior Secured Notes | Second-Lien Notes due 2028, 6.125%
Debt Instrument [Line Items]
Debt redemption percentage					100.00%
Debt redemption, basis spread on discount rate	5000.00%
Debt redemption, additional make-whole charge					1.00%
Redemption prior to February 15, 2023 | Senior Secured Notes | First-Lien Notes due 2025, 6.000%
Debt Instrument [Line Items]
Debt redemption percentage	100.00%
Debt redemption, basis spread on discount rate					5000.00%
Debt redemption, additional make-whole charge	1.00%
Redemption prior to February 15, 2023; limited to 40% of aggregate principal | Senior Secured Notes | Second-Lien Notes due 2028, 6.125%
Debt Instrument [Line Items]
Debt redemption percentage					106.125%
Redemption limitation based on aggregate principal					40.00%
Minimum aggregate principal following redemption					60.00%
Maximum term allowed for redemption following offering					120 days
Redemption prior to February 15, 2023; limited to 40% of aggregate principal | Senior Secured Notes | First-Lien Notes due 2025, 6.000%
Debt Instrument [Line Items]
Debt redemption percentage	106.00%
Redemption limitation based on aggregate principal	40.00%
Minimum aggregate principal following redemption	60.00%
Maximum term allowed for redemption following offering	120 days
Redemption after February 14, 2023 | Senior Secured Notes | Second-Lien Notes due 2028, 6.125%
Debt Instrument [Line Items]
Debt redemption percentage					103.063%
Redemption after February 14, 2023 | Senior Secured Notes | First-Lien Notes due 2025, 6.000%
Debt Instrument [Line Items]
Debt redemption percentage	103.00%
Redemption upon change in control | Senior Secured Notes | Second-Lien Notes due 2028, 6.125%
Debt Instrument [Line Items]
Debt redemption percentage					101.00%
Redemption upon change in control | Senior Secured Notes | First-Lien Notes due 2025, 6.000%
Debt Instrument [Line Items]
Debt redemption percentage	101.00%

Debt Fair Value (Details)

Debt Fair Value (Details) - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Mar. 25, 2020	Feb. 07, 2020	Feb. 05, 2020
Debt Instrument [Line Items]
Payments on debt (original maturities greater than three months) (M)	$ 1,100,000,000	$ 0
Debt instrument, face amount					$ 1,200,000,000
Senior Secured Notes | Second-Lien Notes due 2028, 6.125%
Debt Instrument [Line Items]
Debt, carrying value	$ 1,277,000,000
Debt instrument, face amount				$ 600,000,000
Revolving Credit Facility | Senior Secured Credit Facility | First-Lien Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, face amount			$ 1,000

Debt 144A due 2025 (Details)

Debt 144A due 2025 (Details) - USD ($) $ in Millions	May 13, 2020	Feb. 07, 2020	Feb. 05, 2020	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Debt instrument, face amount			$ 1,200
Proceeds from debt issuance			$ 1,168	$ 2,400	$ 0
Senior Secured Notes | First-Lien Notes due 2025, 6.000%
Debt Instrument [Line Items]
Debt instrument, face amount	$ 700
Fixed interest rate	6.00%
Proceeds from debt issuance	$ 691
Senior Secured Notes | First-Lien Notes due 2025, 6.000% | Minimum
Debt Instrument [Line Items]
Required prior notice for debt redemption, term	10 days
Senior Secured Notes | First-Lien Notes due 2025, 6.000% | Maximum
Debt Instrument [Line Items]
Required prior notice for debt redemption, term	60 days
Senior Secured Notes | First-Lien Notes due 2025, 6.000% | Redemption prior to May 15, 2022
Debt Instrument [Line Items]
Debt redemption percentage	100.00%
Debt redemption, additional make-whole charge	1.00%
Debt redemption, basis spread on discount rate		5000.00%
Senior Secured Notes | First-Lien Notes due 2025, 6.000% | Redemption prior to May 15, 2022; limited to 40% of aggregate principal
Debt Instrument [Line Items]
Debt redemption percentage	106.00%
Redemption limitation based on aggregate principal	40.00%
Minimum aggregate principal following redemption	60.00%
Maximum term allowed for redemption following offering	120 days
Senior Secured Notes | First-Lien Notes due 2025, 6.000% | Redemption after May 14, 2022
Debt Instrument [Line Items]
Debt redemption percentage	103.00%
Senior Secured Notes | First-Lien Notes due 2025, 6.000% | Redemption upon change in control
Debt Instrument [Line Items]
Debt redemption percentage	101.00%

Debt ABL Credit Agreement (Deta

Debt ABL Credit Agreement (Details) - Senior Secured Credit Facility - ABL Credit Agreement - Deutsche Bank AG New York Branch - Revolving Credit Facility - USD ($)	May 13, 2020	Dec. 31, 2020	Sep. 30, 2020
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 800,000,000
Revolving credit facility, additional borrowing capacity, accordion feature	$ 350,000,000
Revolving credit facility, current borrowing capacity			$ 681,000,000
Financial maintenance covenant, percentage of aggregate commitments	10.00%
Financial maintenance covenant, minimum base amount	$ 50,000,000
Financial maintenance covenant, term excess availability exceeds threshold	30 days
Required fixed charge coverage ratio	1
Agent control of cash, percentage of borrowing base	12.50%
Agent control of cash, minimum base amount	$ 62,500,000
Forecast
Line of Credit Facility [Line Items]
Revolving credit facility, current borrowing capacity		$ 678,000,000
Minimum
Line of Credit Facility [Line Items]
Revolving credit facility, commitment fee	0.25%
Agent control of cash, term excess availability exceeds threshold	500.00%
Maximum
Line of Credit Facility [Line Items]
Revolving credit facility, commitment fee	0.375%
Agent control of cash, term excess availability exceeds threshold	3000.00%
Fed funds effective rate and overnight bank funding rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Applicable margin	2.25%
LIBOR | Minimum
Line of Credit Facility [Line Items]
Adjusted LIBO Rate, stated minimum	0.75%
Applicable margin	1.75%
LIBOR | Maximum
Line of Credit Facility [Line Items]
Applicable margin	2.25%
Base Rate
Line of Credit Facility [Line Items]
Applicable margin	1.25%
Base Rate | Minimum
Line of Credit Facility [Line Items]
Applicable margin	0.75%
Base Rate | Maximum
Line of Credit Facility [Line Items]
Applicable margin	1.25%

Acquisitions and Divestitures (

Acquisitions and Divestitures (Details) $ in Millions	Mar. 01, 2020USD ($)employee	Feb. 01, 2020USD ($)employee	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Sales			$ 1,415				$ 1,805	$ 4,213	$ 5,569
Disposed of by sale | Aluminum Rolling Mill in Itapissuma, Brazil
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received		$ 46
Gain (loss) on sale		$ (59)
Total Sales										$ 143	$ 179	$ 162
Number of employees | employee		500
Asset Impairment Charges					$ 6	$ 6	$ 59			53
Disposed of by sale | Hard Alloy Extrusions Plant in South Korea
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received	$ 55
Gain (loss) on sale	31			$ 1
Write-off of goodwill	$ 6
Total Sales										$ 51	$ 53	$ 50
Number of employees | employee	160

Contingencies and Commitments_

Contingencies and Commitments​ (Details)	Jun. 06, 2019plaintiff	Sep. 15, 2017executive	Jun. 30, 2019USD ($)	Sep. 30, 2020USD ($)firefighterspoliceOfficers	Sep. 30, 2020USD ($)firefighterspoliceOfficers	Jun. 26, 2020claimants	Jun. 12, 2020firefighterspoliceOfficersclaimants	Jun. 11, 2020firefighters	Dec. 31, 2019USD ($)
Site Contingency [Line Items]
Environmental remediation				$ 181,000,000	$ 181,000,000				$ 208,000,000
Environmental remediation, current				97,000,000	97,000,000				83,000,000
Environmental remediation, payments				33,000,000	54,000,000
Accrual for Environmental Loss Contingencies, Increase (Decrease) for Acquisitions and Divestitures					13,000,000
Accrual for Environmental Loss Contingencies, Period Increase (Decrease)				$ 1,000,000	$ 3,000,000
Loss Contingency, Number of Firefighters | firefighters				1	1		2	80
Accrual for Environmental Loss Contingencies, Revision in Estimates					$ 5,000,000
Loss Contingency, Number of Police Officers | policeOfficers				37	37		27
Site Remediation Systems [Member]
Site Contingency [Line Items]
Environmental remediation, additions				$ (1,000,000)
Unpaid Invoices [Member]
Site Contingency [Line Items]
Accounts Payable, Trade									22,000,000
Other Environmental [Member]
Site Contingency [Line Items]
Accrual for Environmental Loss Contingencies, Period Increase (Decrease)					$ (5,000,000)
Aluminum Rolling Mill in Itapissuma, Brazil
Site Contingency [Line Items]
Environmental remediation, additions					(1,000,000)
Behrens v. Arconic
Site Contingency [Line Items]
Number of plaintiffs | plaintiff	247
Sullivan v. Arconic
Site Contingency [Line Items]
Number of former executives | executive		3
Birnberg Peirce Ltd [Member]
Site Contingency [Line Items]
Loss Contingency, Number of Claimants | claimants							4
Howe & Co Solicitors [Member]
Site Contingency [Line Items]
Loss Contingency, Number of Claimants | claimants							2
Russell-Cooke LLP [Member]
Site Contingency [Line Items]
Loss Contingency, Number of Claimants | claimants						3
Massena West, NY
Site Contingency [Line Items]
Environmental remediation				$ 131,000,000	$ 131,000,000				171,000,000
Environmental remediation, additions			$ (25,000,000)
Accounts Payable, Trade									$ 21,000,000

Subsequent Events_ (Details)

Subsequent Events​ (Details) $ in Millions	May 13, 2020USD ($)	Apr. 02, 2020USD ($)	Oct. 30, 2020USD ($)	Mar. 01, 2020USD ($)	Dec. 31, 2019USD ($)	Feb. 08, 2019company	Oct. 01, 2018USD ($)claimants
Subsequent Event [Line Items]
Number of publicly traded companies | company						2
Disposed of by sale | Hard Alloy Extrusions Plant in South Korea
Subsequent Event [Line Items]
Consideration received				$ 55
Disposed of by sale | Texarkana Rolling Mill and Cast House [Member]
Subsequent Event [Line Items]
Consideration received							$ 302
Disposal Group, Including Discontinued Operation, Book Value							$ 63
Period of Operationalizing Rolling Mill Equipment of Transaction | claimants							36
Disposed of by sale | Texarkana Rolling Mill and Cast House [Member] | Achievement of Milestones [Member]
Subsequent Event [Line Items]
Consideration received					$ 25		$ 50
Disposed of by sale | Texarkana Rolling Mill and Cast House [Member] | Achievement of Milestones [Member] | Subsequent events
Subsequent Event [Line Items]
Consideration received			$ 25
Senior Secured Credit Facility | First-Lien Revolving Credit Facility | Revolving Credit Facility
Subsequent Event [Line Items]
Proceeds from revolving credit facility	$ 500	$ 500