Segment Information - Schedule of Segment Adjusted EBITDA to Consolidated Net Income (Loss) Attributable to Alcoa Corporation (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Segment Reporting Information [Line Items]
Total Segment Adjusted EBITDA	$ 236	$ 419	$ 1,034	$ 608
Transformation	(21)	(16)	(33)	(30)
Intersegment eliminations	135	(29)	238	(37)
Corporate expenses	(45)	(41)	(82)	(75)
Provision for depreciation, depletion, and amortization	(153)	(163)	(301)	(324)
Restructuring and other charges, net (D)	(14)	(18)	(19)	(220)
Interest expense	(56)	(40)	(109)	(67)
Other income (expenses), net (P)	112	22	138	(37)
Other	(33)	(42)	(37)	(51)
Consolidated income (loss) before income taxes	161	92	829	(233)
Provision for income taxes	(10)	(61)	(130)	(43)
Net loss (income) attributable to noncontrolling interest	13	(11)	13	44
NET INCOME (LOSS) ATTRIBUTABLE TO ALCOA CORPORATION	$ 164	$ 20	$ 712	$ (232)