Segment Information - Schedule of Sales by Product Division (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation Of Revenue [Line Items]
Sales	$ 2,684	$ 3,644	$ 5,354	$ 6,937
Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales	1,824	2,624	3,670	5,071
Alumina [Member]
Disaggregation Of Revenue [Line Items]
Sales	774	1,064	1,488	1,914
Energy [Member]
Disaggregation Of Revenue [Line Items]
Sales	26	40	54	81
Bauxite [Member]
Disaggregation Of Revenue [Line Items]
Sales	109	27	236	55
Other [Member]
Disaggregation Of Revenue [Line Items]
Sales	$ (49)	$ (111)	$ (94)	$ (184)