Investments - Summary of Unaudited Financial Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Schedule Of Equity Method Investments [Line Items]
Net income (loss)	$ 31	$ (307)	$ (121)	$ (232)	$ (276)	$ (353)
Ma'aden Joint Venture [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	804		700		1,515	1,300
Cost of goods sold	613		620		1,212	1,302
Net income (loss)	102		(99)		94	(351)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	26		(25)		24	(88)
Other	(4)		(3)		(12)	(15)
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	22		(28)		12	(103)
Mining [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	158		172		273	359
Cost of goods sold	104		101		207	204
Net income (loss)	14		14		9	38
Equity in net income (loss) of affiliated companies, before reconciling adjustments	6		6		4	17
Other	0		1		0	1
Mining [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	6		7		4	18
Energy [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	59		59		122	117
Cost of goods sold	25		32		50	59
Net income (loss)	29		22		60	46
Equity in net income (loss) of affiliated companies, before reconciling adjustments	11		9		23	18
Other	0		1		(1)	1
Energy [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	11		10		22	19
Other [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	114		116		229	237
Cost of goods sold	104		106		209	219
Net income (loss)	(20)		(33)		(36)	(49)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(9)		(15)		(17)	(23)
Other	12		7		7	0
Other [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	$ 3		$ (8)		$ (10)	$ (23)