Statement of Changes in Consolidated Mezzanine Equity and Equity (unaudited) - USD ($) $ in Millions	Total	Non-controlling Interest [Member]	Common Stock [Member]	Additional Capital [Member]	Accumulated Deficit [Member]	Accumulated other comprehensive (loss) income [Member]	Non-controlling Interest [Member]
Balance at Dec. 31, 2023	$ 5,845		$ 2	$ 9,187	$ (1,293)	$ (3,645)	$ 1,594
Net (loss) income	(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
Other comprehensive income (loss) (G)	(157)
Other comprehensive income (loss) (G)	(92)
Balance at Jun. 30, 2024	5,416		2	9,196	(1,562)	(3,737)	1,517
Balance at Mar. 31, 2024	5,534		2	9,184	(1,564)	(3,628)	1,540
Net (loss) income	31				20		11
Other comprehensive income (loss) (G)	(121)					(109)	(12)
Other comprehensive income (loss) (G)	(109)
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
Balance at Dec. 31, 2024	5,157		3	11,587	(1,323)	(5,110)
Balance at Dec. 31, 2024	0	$ 0
Net (loss) income	548				548
Other comprehensive income (loss) (G)	206					206
Stock-based compensation	11			11
Net effect of tax withholding for compensation plans and exercise of stock options	(5)			(5)
Dividends paid on Alcoa preferred stock ($0.10 per share)	0				0
Dividends paid on Alcoa common stock ($0.10 per share)	(26)				(26)
Joint venture formation (C)	(76)	103		(45)		(31)
Balance at Mar. 31, 2025	5,815		3	11,548	(801)	(4,935)
Balance at Mar. 31, 2025		103
Balance at Dec. 31, 2024	5,157		3	11,587	(1,323)	(5,110)
Balance at Dec. 31, 2024	0	0
Other comprehensive income (loss) (G)	387
Other comprehensive income (loss) (G)	377
Dividends paid on Alcoa preferred stock ($0.10 per share)	(1)
Balance at Jun. 30, 2025	6,135		3	11,560	(664)	(4,764)
Balance at Jun. 30, 2025	100	100
Balance at Mar. 31, 2025	5,815		3	11,548	(801)	(4,935)
Balance at Mar. 31, 2025		103
Net (loss) income	164	(13)			164
Other comprehensive income (loss) (G)	181
Other comprehensive income (loss) (G)	171	10				171
Stock-based compensation	12			12
Dividends paid on Alcoa preferred stock ($0.10 per share)	(1)				(1)
Dividends paid on Alcoa common stock ($0.10 per share)	(26)				(26)
Balance at Jun. 30, 2025	6,135		$ 3	$ 11,560	$ (664)	$ (4,764)
Balance at Jun. 30, 2025	$ 100	$ 100