Segment Information - Schedule of Segment Adjusted EBITDA to Consolidated Net Income Attributable to Alcoa Corporation (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Total Segment Adjusted EBITDA	$ 569	$ 375
Transformation	(11)	(16)
Intersegment eliminations	(7)	(8)
Corporate expenses	(26)	(27)
Provision for depreciation, depletion, and amortization	(182)	(170)
Restructuring and other charges, net (D)	(7)	(2)
Interest expense	(42)	(30)
Other income, net (Q)	24	132
Income before income taxes	312	219
Provision for income taxes	(93)	(80)
Net income attributable to noncontrolling interest	(44)	(59)
NET INCOME ATTRIBUTABLE TO ALCOA CORPORATION	175	80
Other [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges, net (D)	(7)	(2)
Other	$ (6)	$ (35)