Segment Information - Schedule of Sales by Product Division (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation Of Revenue [Line Items]
Sales	$ 3,293	$ 2,870
Primary Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales	2,447	1,727
Alumina [Member]
Disaggregation Of Revenue [Line Items]
Sales	850	760
Flat-Rolled Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales		320
Energy [Member]
Disaggregation Of Revenue [Line Items]
Sales	41	39
Bauxite [Member]
Disaggregation Of Revenue [Line Items]
Sales	28	52
Other Products [Member]
Disaggregation Of Revenue [Line Items]
Sales	$ (73)	$ (28)