Investments - Summary of Unaudited Financial Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Schedule Of Equity Method Investments [Line Items]
Net income (loss)	$ (121)	$ (232)	$ 674	$ 553	$ (353)	$ 1,227
Ma'aden Joint Venture [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	700		1,016		1,300	1,913
Cost of goods sold	620		712		1,302	1,328
Net income (loss)	(99)		156		(351)	311
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(25)		39		(88)	78
Other	(3)		(4)		(15)	(4)
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	(28)		35		(103)	74
Mining [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	172		191		359	422
Cost of goods sold	101		123		204	269
Net income (loss)	14		32		38	81
Equity in net income (loss) of affiliated companies, before reconciling adjustments	6		12		17	26
Other	1		(2)		1	(2)
Mining [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	7		10		18	24
Energy [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	59		65		117	127
Cost of goods sold	32		23		59	53
Net income (loss)	22		29		46	52
Equity in net income (loss) of affiliated companies, before reconciling adjustments	9		12		18	21
Other	1		(2)		1	(1)
Energy [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	10		10		19	20
Other [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	116		125		237	242
Cost of goods sold	106		115		219	222
Net income (loss)	(33)		(30)		(49)	(58)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(15)		(15)		(23)	(28)
Other	7		19		0	15
Other [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	$ (8)		$ 4		$ (23)	$ (13)