Investments - Summary of Unaudited Financial Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Schedule of Equity Method Investments [Line Items]
Net (loss) income	$ (769)	$ 674	$ 553	$ 370	$ 350	$ 219	$ 458	$ 939
Ma'aden Joint Venture [Member] | Alcoa Corporation [Member]
Schedule of Equity Method Investments [Line Items]
Alcoa Corporation’s equity in net income (loss) of affiliated companies	(25)			35			49	68
Ma'aden Joint Venture [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Sales	773			776			2,686	2,199
Cost of goods sold	692			479			2,020	1,490
Net (loss) income	(94)			152			217	299
Equity in net (loss) income of affiliated companies, before reconciling adjustments	(24)			38			54	75
Other	(1)			(3)			(5)	(7)
Mining [Member] | Alcoa Corporation [Member]
Schedule of Equity Method Investments [Line Items]
Alcoa Corporation’s equity in net income (loss) of affiliated companies	7			5			31	14
Mining [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Sales	167			198			589	568
Cost of goods sold	101			145			370	414
Net (loss) income	14			11			95	31
Equity in net (loss) income of affiliated companies, before reconciling adjustments	7			6			33	16
Other				(1)			(2)	(2)
Energy [Member] | Alcoa Corporation [Member]
Schedule of Equity Method Investments [Line Items]
Alcoa Corporation’s equity in net income (loss) of affiliated companies	8			8			28	29
Energy [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Sales	66			73			193	188
Cost of goods sold	38			51			91	108
Net (loss) income	28			22			80	74
Equity in net (loss) income of affiliated companies, before reconciling adjustments	11			8			32	29
Other	(3)						(4)
Other [Member] | Alcoa Corporation [Member]
Schedule of Equity Method Investments [Line Items]
Alcoa Corporation’s equity in net income (loss) of affiliated companies	(8)			(1)			(21)	7
Other [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Sales	121			100			363	291
Cost of goods sold	110			90			332	261
Net (loss) income	(19)			(12)			(77)	(18)
Equity in net (loss) income of affiliated companies, before reconciling adjustments	(9)			(5)			(37)	(8)
Other	$ 1			$ 4			$ 16	$ 15