Segment Information - Schedule of Sales by Product Division (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation Of Revenue [Line Items]
Sales	$ 3,644	$ 2,833	$ 6,937	$ 5,703
Primary Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales	2,624	2,112	5,071	3,839
Alumina [Member]
Disaggregation Of Revenue [Line Items]
Sales	1,064	684	1,914	1,444
Flat-Rolled Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales				320
Energy [Member]
Disaggregation Of Revenue [Line Items]
Sales	40	49	81	88
Bauxite [Member]
Disaggregation Of Revenue [Line Items]
Sales	27	34	55	86
Other Products [Member]
Disaggregation Of Revenue [Line Items]
Sales	$ (111)	$ (46)	$ (184)	$ (74)