Investments - Summary of Unaudited Financial Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Schedule Of Equity Method Investments [Line Items]
Net income (loss)	$ (232)	$ 553
Ma'aden Joint Venture [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	600	897
Cost of goods sold	682	616
Net income (loss)	(252)	155
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(63)	39
Other	(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	(75)	39
Mining [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	187	231
Cost of goods sold	103	146
Net income (loss)	24	49
Equity in net income (loss) of affiliated companies, before reconciling adjustments	11	14
Mining [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	11	14
Energy [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	58	62
Cost of goods sold	27	30
Net income (loss)	24	23
Equity in net income (loss) of affiliated companies, before reconciling adjustments	9	9
Other		1
Energy [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	9	10
Other [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	121	117
Cost of goods sold	113	107
Net income (loss)	(16)	(28)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(8)	(13)
Other	(7)	(4)
Other [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	$ (15)	$ (17)