Statement of Changes in Consolidated Equity (unaudited) - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Capital [Member]	Accumulated Deficit [Member]	Accumulated other comprehensive (loss) income [Member]	Non-controlling Interest [Member]
Balance at Dec. 31, 2022	$ 6,589	$ 2	$ 9,183	$ (570)	$ (3,539)	$ 1,513
Net income (loss)	(232)			(231)		(1)
Other comprehensive income (loss) (G)	(101)				(116)	15
Stock-based compensation	10		10
Net effect of tax withholding for compensation plans and exercise of stock options	(33)		(33)
Dividends paid on Alcoa common stock ($0.10 per share)	(18)			(18)
Contributions	86					86
Distributions	(6)					(6)
Other	1		2			(1)
Balance at Mar. 31, 2023	6,296	2	9,162	(819)	(3,655)	1,606
Balance at Dec. 31, 2022	6,589	2	9,183	(570)	(3,539)	1,513
Net income (loss)	(546)
Other comprehensive income (loss) (G)	(32)
Balance at Sep. 30, 2023	6,092	2	9,179	(1,125)	(3,547)	1,583
Balance at Mar. 31, 2023	6,296	2	9,162	(819)	(3,655)	1,606
Net income (loss)	(121)			(102)		(19)
Other comprehensive income (loss) (G)	270				261	9
Stock-based compensation	11		11
Dividends paid on Alcoa common stock ($0.10 per share)	(18)			(18)
Contributions	36					36
Distributions	(16)					(16)
Balance at Jun. 30, 2023	6,458	2	9,173	(939)	(3,394)	1,616
Net income (loss)	(193)			(168)		(25)
Other comprehensive income (loss) (G)	(201)				(153)	(48)
Stock-based compensation	6		6
Dividends paid on Alcoa common stock ($0.10 per share)	(18)			(18)
Contributions	42					42
Distributions	(2)					(2)
Balance at Sep. 30, 2023	6,092	2	9,179	(1,125)	(3,547)	1,583
Balance at Dec. 31, 2023	5,845	2	9,187	(1,293)	(3,645)	1,594
Net income (loss)	(307)			(252)		(55)
Other comprehensive income (loss) (G)	(36)				17	(53)
Stock-based compensation	10		10
Net effect of tax withholding for compensation plans and exercise of stock options	(15)		(15)
Dividends paid on Alcoa common stock ($0.10 per share)	(19)			(19)
Contributions	61					61
Distributions	(6)					(6)
Other	1		2			(1)
Balance at Mar. 31, 2024	5,534	2	9,184	(1,564)	(3,628)	1,540
Balance at Dec. 31, 2023	5,845	2	9,187	(1,293)	(3,645)	1,594
Net income (loss)	(178)
Other comprehensive income (loss) (G)	(99)
Balance at Sep. 30, 2024	5,250	3	11,487	(1,498)	(4,742)
Balance at Mar. 31, 2024	5,534	2	9,184	(1,564)	(3,628)	1,540
Net income (loss)	31			20		11
Other comprehensive income (loss) (G)	(121)				(109)	(12)
Stock-based compensation	12		12
Dividends paid on Alcoa common stock ($0.10 per share)	(18)			(18)
Contributions	4					4
Distributions	(26)					(26)
Balance at Jun. 30, 2024	5,416	2	9,196	(1,562)	(3,737)	1,517
Net income (loss)	98			90		8
Other comprehensive income (loss) (G)	58				94	(36)
Stock-based compensation	9		9
Dividends paid on Alcoa common stock ($0.10 per share)	(26)			(26)
Distributions	(17)					(17)
Acquisition of noncontrolling interest (C)	(288)	1	2,282		(1,099)	$ (1,472)
Balance at Sep. 30, 2024	$ 5,250	$ 3	$ 11,487	$ (1,498)	$ (4,742)