XML 538 R155.htm IDEA: XBRL DOCUMENT v3.25.0.1
Financial instruments and risk management - Summary of notional aluminum forward sales contracts embedded in power contracts (Detail)
$ in Millions
Dec. 31, 2024
USD ($)
t
uSDollarPerTonne
Dec. 31, 2023
USD ($)
t
uSDollarPerTonne
Disclosure of detailed information about financial instruments [line items]    
Nominal amount (tonnes) | t 359,572 428,686
Nominal amount (US$ millions) | $ $ 890 $ 1,050
Average hedged rate (US$ per tonne) | uSDollarPerTonne 2,474 2,449
Due within 1 year    
Disclosure of detailed information about financial instruments [line items]    
Nominal amount (tonnes) | t 73,117 72,617
Nominal amount (US$ millions) | $ $ 174 $ 169
Average hedged rate (US$ per tonne) | uSDollarPerTonne 2,382 2,331
Between 1 and 5 years    
Disclosure of detailed information about financial instruments [line items]    
Nominal amount (tonnes) | t 286,455 289,801
Nominal amount (US$ millions) | $ $ 716 $ 711
Average hedged rate (US$ per tonne) | uSDollarPerTonne 2,498 2,452
Between 5 and 10 years    
Disclosure of detailed information about financial instruments [line items]    
Nominal amount (tonnes) | t 0 66,268
Nominal amount (US$ millions) | $ $ 0 $ 170
Average hedged rate (US$ per tonne) | uSDollarPerTonne 0 2,564