v3.26.1
Segment Information - Schedule of Third-party Sales by Product Division (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Disaggregation Of Revenue [Line Items]        
Sales $ 3,966 $ 3,018 $ 7,159 $ 6,387
Aluminum [Member]        
Disaggregation Of Revenue [Line Items]        
Sales 3,446 1,993 6,028 3,948
Alumina [Member]        
Disaggregation Of Revenue [Line Items]        
Sales 538 830 1,059 2,041
Bauxite [Member]        
Disaggregation Of Revenue [Line Items]        
Sales 76 203 194 445
Energy [Member]        
Disaggregation Of Revenue [Line Items]        
Sales 52 38 129 71
Other [Member]        
Disaggregation Of Revenue [Line Items]        
Sales $ (146) $ (46) $ (251) $ (118)