Investments - Summary of Profit and Loss Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Net income (loss)	$ 24	$ (773)	$ 38
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	13	(158)	4
Ma'aden Joint Venture [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Sales	3,328	2,726	3,317
Cost of goods sold	2,681	2,550	2,696
Net income (loss)	134	(457)	42
Equity in net income (loss) of affiliated companies, before reconciling adjustments	34	(115)	11
Other	(21)	(43)	(7)
Mining [Member] | Alcoa Corporation [Member]
Schedule of Equity Method Investments [Line Items]
Alcoa Corporation's equity in net income (loss) of affiliated companies	12	23	37
Mining [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Sales	573	670	763
Cost of goods sold	432	446	488
Net income (loss)	26	50	110
Equity in net income (loss) of affiliated companies, before reconciling adjustments	12	23	39
Other	0	0	(2)
Energy [Member] | Alcoa Corporation [Member]
Schedule of Equity Method Investments [Line Items]
Alcoa Corporation's equity in net income (loss) of affiliated companies	38	40	38
Energy [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Sales	240	236	252
Cost of goods sold	107	118	120
Net income (loss)	112	100	109
Equity in net income (loss) of affiliated companies, before reconciling adjustments	44	39	41
Other	(6)	1	(3)
Other [Member] | Alcoa Corporation [Member]
Schedule of Equity Method Investments [Line Items]
Alcoa Corporation's equity in net income (loss) of affiliated companies	(23)	(55)	(21)
Other [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Sales	463	464	488
Cost of goods sold	419	425	445
Net income (loss)	(68)	(97)	(75)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(32)	(46)	(36)
Other	$ 9	$ (9)	$ 15