Segment and Related Information - Schedule of Segment Adjusted EBITDA to Consolidated Net (Loss) Income Attributable to Alcoa Corporation (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total Segment Adjusted EBITDA									$ 1,626	$ 3,250	$ 2,739
Transformation									(7)	(3)	(49)
Intersegment eliminations									150	(8)	(80)
Corporate expenses									(101)	(96)	(131)
Provision for depreciation, depletion, and amortization									(713)	(733)	(750)
Restructuring and other charges, net (D)									(1,031)	(527)	(309)
Interest expense (T)									(121)	(122)	(104)
Other expenses, net (T)									(162)	(64)	(27)
(Loss) income before income taxes									(438)	1,625	1,200
Provision for income taxes (P)									(415)	(732)	(592)
Net income attributable to noncontrolling interest									(272)	(643)	(329)
Net (loss) income attributable to Alcoa Corporation (I)	$ (303)	$ (221)	$ (402)	$ (199)	$ 51	$ (6)	$ 10	$ 195	(1,125)	250	279
Other [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges, net (D)									(1,031)	(527)	(309)
Interest expense (T)									(121)	(122)	(104)
Other									$ (79)	$ (72)	$ (89)