v3.26.1
Restructuring and Other Charges, Net - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Restructuring Cost and Reserve [Line Items]          
Restructuring And Other Charges $ (4) $ 14 $ 14 $ 19  
Restructuring and other charges, net (4) 14 14 19  
Alcoa Corporation [Member]          
Restructuring Cost and Reserve [Line Items]          
Noncurrent portion of the reserve 20   20   $ 34
2025 Restructuring Plans Action [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring and other charges, net   14   19  
2026 Restructuring Plans Action [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring and other charges, net (4)   14    
Certain Employee Obligations [Member] | 2025 Restructuring Plans Action [Member] | San Ciprian (Spain) Aluminum Smelter [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring And Other Charges   6   9  
Contract Costs [Member] | 2025 Restructuring Plans Action [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring and other charges, net   (12)   (10)  
Contract Costs [Member] | 2026 Restructuring Plans Action [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring and other charges, net (13)   5    
Net Additional Asset Retirement Obligations and Environmental Remediation [Member] | 2025 Restructuring Plans Action [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring and other charges, net   $ 20   $ 20  
Net Additional Asset Retirement Obligations and Environmental Remediation [Member] | 2026 Restructuring Plans Action [Member]          
Restructuring Cost and Reserve [Line Items]          
Restructuring and other charges, net $ 9   $ 9