Segment Information - Schedule of Sales by Product Division (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation Of Revenue [Line Items]
Sales	$ 2,599	$ 2,670
Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales	1,661	1,846
Alumina [Member]
Disaggregation Of Revenue [Line Items]
Sales	890	714
Energy [Member]
Disaggregation Of Revenue [Line Items]
Sales	33	28
Bauxite [Member]
Disaggregation Of Revenue [Line Items]
Sales	61	127
Other [Member]
Disaggregation Of Revenue [Line Items]
Sales	$ (46)	$ (45)