Contingencies and Commitments - Commitments (Details) - USD ($) $ in Millions	1 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Loss Contingencies [Line Items]
Purchase obligations due in 2024	$ 244
Purchase obligations due in 2025	32
Purchase obligations due in 2026	11
Purchase obligations due in 2027	0
Purchase obligations due in 2028	0
Purchase obligations due thereafter	0
Guarantees of third party related to project financing	24
Combined fair value of guarantees	6	$ 6
Insurance annual coverage limit	80	80	$ 80
Total amount committed under outstanding surety bonds	43
Amount of outstanding surety bonds relating to these liabilities	21
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount committed	52
Arconic Corporation Environmental Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount committed	17
Letter of Credit
Loss Contingencies [Line Items]
Maximum borrowing capacity	114
Other Noncurrent Liabilities and Deferred Credits | Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	$ 1,131	$ 1,040