v3.26.1
Contingencies - Additional Information - 1 (Detail) - Alcoa World Alumina Brasil [Member] - Brazilian Federal Revenue Office [Member]
R$ in Millions, $ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2026
USD ($)
Jun. 30, 2026
BRL (R$)
Dec. 31, 2013
USD ($)
Dec. 31, 2013
BRL (R$)
Dec. 31, 2024
USD ($)
Dec. 31, 2024
BRL (R$)
Dec. 31, 2013
BRL (R$)
Dec. 31, 2012
USD ($)
Dec. 31, 2012
BRL (R$)
Loss Contingencies [Line Items]                  
Disallowed tax credits     $ 110   $ 19 R$ 92 R$ 220    
Value added tax receivable     $ 41 R$ 82          
Federal value added tax credits               $ 136 R$ 273
Charge recorded in provision for income taxes to establish liability for estimated loss | R$   R$ 312              
Minimum [Member]                  
Loss Contingencies [Line Items]                  
Charge recorded in provision for income taxes to establish liability for estimated loss $ 0                
Maximum [Member]                  
Loss Contingencies [Line Items]                  
Charge recorded in provision for income taxes to establish liability for estimated loss $ 60