Contingencies and Commitments - Commitments (Details) - USD ($) $ in Millions	1 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Purchase obligations due in 2022	$ 229
Purchase obligations due in 2023	95
Purchase obligations due in 2024	80
Purchase obligations due in 2025	2
Purchase obligations due in 2026	0
Purchase obligations due thereafter	0
Guarantees of third party related to project financing	15
Combined fair value of guarantees	6	$ 12
Insurance annual coverage limit	80
Total amount committed under outstanding surety bonds	47
Amount of outstanding surety bonds relating to these liabilities	25
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount committed	53
Arconic Corporation Environmental Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount committed	17
Arconic Corporation Environmental Obligations | Letters Of Credit Pending Cancellation
Loss Contingencies [Line Items]
Letters of credit, total amount committed	1
Bank Loan Obligations
Loss Contingencies [Line Items]
Letters of credit	119
Separation Agreement | Other Noncurrent Liabilities and Deferred Credits
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	$ 1,406	$ 1,398