Investments - Summary of Unaudited Financial Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Schedule Of Equity Method Investments [Line Items]
Net income (loss)	$ (193)	$ (121)	$ (232)	$ (769)	$ 674	$ 553	$ (546)	$ 458
Ma'aden Joint Venture [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	725			773			2,025	2,686
Cost of goods sold	645			692			1,947	2,020
Net income (loss)	(39)			(94)			(390)	217
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(10)			(24)			(98)	54
Other	(15)			(1)			(30)	(5)
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	(25)			(25)			(128)	49
Mining [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	157			167			516	589
Cost of goods sold	121			101			325	370
Net income (loss)	6			14			44	95
Equity in net income (loss) of affiliated companies, before reconciling adjustments	3			7			20	33
Other	0			0			1	(2)
Mining [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	3			7			21	31
Energy [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	61			66			178	193
Cost of goods sold	28			38			87	91
Net income (loss)	31			28			77	80
Equity in net income (loss) of affiliated companies, before reconciling adjustments	12			11			30	32
Other	(2)			(3)			(1)	(4)
Energy [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	10			8			29	28
Other [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule Of Equity Method Investments [Line Items]
Sales	117			121			354	363
Cost of goods sold	105			110			324	332
Net income (loss)	(21)			(19)			(70)	(77)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(11)			(9)			(34)	(37)
Other	(6)			1			(6)	16
Other [Member] | Alcoa Corporation [Member]
Schedule Of Equity Method Investments [Line Items]
Alcoa Corporations equity in net income (loss) of affiliated companies	$ (17)			$ (8)			$ (40)	$ (21)