Segment Information - Schedule of Sales by Product Division (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation Of Revenue [Line Items]
Sales	$ 2,906	$ 2,684	$ 5,505	$ 5,354
Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales	1,934	1,824	3,595	3,670
Alumina [Member]
Disaggregation Of Revenue [Line Items]
Sales	904	774	1,794	1,488
Energy [Member]
Disaggregation Of Revenue [Line Items]
Sales	29	26	62	54
Bauxite [Member]
Disaggregation Of Revenue [Line Items]
Sales	96	109	157	236
Other [Member]
Disaggregation Of Revenue [Line Items]
Sales	$ (57)	$ (49)	$ (103)	$ (94)