Income Taxes - Reconciliation of U.S. Federal Statutory Rate to Arconic's Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
U.S. federal statutory rate	21.00%	21.00%	21.00%
Foreign tax rate differential	(0.70%)	(1.20%)	10.90%
U.S. and residual tax on foreign earnings	6.50%	5.60%	15.30%
U.S. State and local taxes	1.00%	2.20%	0.80%
Federal (cost) benefit of state tax	(0.30%)	(2.00%)	1.20%
Permanent differences related to asset disposals and items included in restructuring and other charges	(0.30%)	6.80%	(1.30%)
Non-deductible officer compensation	1.60%	3.50%	4.90%
Statutory tax rate and law changes	1.00%	(15.90%)	(0.60%)
Tax holidays	(0.40%)	(0.40%)	(8.20%)
Tax credits	(10.40%)	(0.40%)	(1.30%)
Changes in valuation allowances	5.10%	74.80%	(52.20%)
Changes in uncertain tax positions	0.00%	(116.90%)	0.30%
Prior year tax adjustments	(3.70%)	(1.70%)	44.30%
Other	0.00%	1.20%	4.90%
Effective tax rate	20.40%	(23.40%)	40.00%
Tax law change expense (benefit)		$ (30)
Benefit for income tax credits related to development incentives in Hungary	$ 32
Favorable spanish tax case decision		104
Foreign tax credits amount released			$ 112
Reserve liability		64
Tax position expense (benefit)		$ (30)
Write off			112
Tax expense (benefit) deduction			$ 24

Deferred Tax Assets, Valuation Allowance, Favorable Spanish Tax Case Decision

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Deferred Tax Assets, Valuation Allowance, Foreign Tax Credits, Amount Released

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Deferred Tax Assets Write Off

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Effective Income Tax Rate Reconciliation, Federal Benefit of State Taxes, Percent

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Effective Income Tax Rate Reconciliation, Reserve Liability

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Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Development Incentives, Amount

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Effective Income Tax Reconciliation, United States And Residual Tax On Foreign Earnings, Percent

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to revisions of previously reported income tax expense.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to income tax contingencies. Includes, but not limited to, domestic tax contingency, foreign tax contingency, state and local tax contingency, and other contingencies.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates.

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Amount of increase (decrease) in unrecognized tax benefits attributable to uncertain tax positions taken in tax returns.

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