Investments - Summary of Unaudited Financial Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Schedule Of Equity Method Investments [Line Items]
Net (loss) income	$ (307)	$ (232)
Ma'aden Joint Venture [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	711	600
Cost of goods sold	599	682
Net (loss) income	(8)	(252)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(2)	(63)
Other	(8)	(12)
Alcoa Corporation [Member] | Ma'aden Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	(10)	(75)
Mining [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	115	187
Cost of goods sold	103	103
Net (loss) income	(5)	24
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(2)	11
Other	0	0
Mining [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	(2)	11
Energy [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	63	58
Cost of goods sold	25	27
Net (loss) income	31	24
Equity in net income (loss) of affiliated companies, before reconciling adjustments	12	9
Other	(1)	0
Energy [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	11	9
Other [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	115	121
Cost of goods sold	105	113
Net (loss) income	(16)	(16)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(8)	(8)
Other	(5)	(7)
Other [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	$ (13)	$ (15)