Segment and Related Information - Schedule of Third-party Sales by Product Division (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation Of Revenue [Line Items]
Sales	$ 11,895	$ 10,551	$ 12,451
Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales	7,359	7,045	8,887
Alumina [Member]
Disaggregation Of Revenue [Line Items]
Sales	4,246	3,103	3,478
Bauxite [Member]
Disaggregation Of Revenue [Line Items]
Sales	376	466	168
Energy [Member]
Disaggregation Of Revenue [Line Items]
Sales	147	118	201
Other [Member]
Disaggregation Of Revenue [Line Items]
Sales	$ (233)	$ (181)	$ (283)