Investments - Summary of Balance Sheet Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Current assets	$ 4,914	$ 4,405
Current liabilities	3,395	3,030
Ma'aden Joint Venture [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	1,456	1,433
Noncurrent assets	7,035	6,958
Current liabilities	1,227	1,444
Noncurrent liabilities	4,534	4,272
Mining [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	4	8
Noncurrent assets	454	419
Current liabilities	4	5
Noncurrent liabilities	35	24
Energy [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	99	103
Noncurrent assets	240	310
Current liabilities	16	16
Noncurrent liabilities	35	34
Other [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	177	181
Noncurrent assets	777	764
Current liabilities	85	89
Noncurrent liabilities	$ 120	$ 117