Segment Information - Schedule of Segment Adjusted EBITDA to Consolidated Net (Loss) Income Attributable to Alcoa Corporation (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Total Segment Adjusted EBITDA	$ 400	$ 850	$ 1,286	$ 2,507
Transformation	(6)	1	(1)	(2)
Intersegment eliminations	25	21	110	(55)
Corporate expenses	(27)	(22)	(79)	(75)
Provision for depreciation, depletion, and amortization	(184)	(173)	(530)	(559)
Restructuring and other charges, net (C)	(185)	(177)	(668)	(389)
Interest expense	(30)	(33)	(90)	(91)
Other expenses, net (N)	(27)	(2)	(118)	(32)
(Loss) income before income taxes	(52)	455	(137)	1,235
Provision for income taxes	(95)	(260)	(361)	(569)
Net income attributable to noncontrolling interest	(74)	(201)	(324)	(467)
NET (LOSS) INCOME ATTRIBUTABLE TO ALCOA CORPORATION	(221)	(6)	(822)	199
Other [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges, net (C)	(185)	(177)	(668)	(389)
Interest expense	(30)	(33)	(90)	(91)
Other	$ (18)	$ (10)	$ (47)	$ (69)