Segment Information - Schedule of Sales by Product Division (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation Of Revenue [Line Items]
Sales	$ 2,851	$ 3,109	$ 9,788	$ 8,812
Primary Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales	1,990	2,255	7,033	6,094
Alumina [Member]
Disaggregation Of Revenue [Line Items]
Sales	821	752	2,735	2,196
Flat-Rolled Aluminum [Member]
Disaggregation Of Revenue [Line Items]
Sales				320
Energy [Member]
Disaggregation Of Revenue [Line Items]
Sales	74	117	155	205
Bauxite [Member]
Disaggregation Of Revenue [Line Items]
Sales	52	52	107	138
Other Products [Member]
Disaggregation Of Revenue [Line Items]
Sales	$ (86)	$ (67)	$ (242)	$ (141)