Segment Information - Schedule of Segment Adjusted EBITDA to Consolidated Net (Loss) Income Attributable to Alcoa Corporation (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Total Segment Adjusted EBITDA	$ 402	$ 689
Transformation	2	(2)
Intersegment eliminations	86	76
Corporate expenses	(24)	(27)
Provision for depreciation, depletion, and amortization	(172)	(194)
Interest expense	(30)	(26)
Other expenses, net (N)	(41)	(21)
Income before income taxes	92	491
Provision for income taxes	(150)	(151)
Net income attributable to noncontrolling interest	(141)	(145)
NET (LOSS) INCOME ATTRIBUTABLE TO ALCOA CORPORATION	(199)	195
Other [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges, net (C)	(113)	19
Interest expense	(30)	(26)
Other	$ (18)	$ (23)