XML 539 R156.htm IDEA: XBRL DOCUMENT v3.25.0.1
Financial instruments and risk management - Summary of impact of hedging instrument on statement of financial position (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Disclosure of detailed information about financial instruments [line items]      
Nominal amount (US$ millions) $ 890 $ 1,050  
Change in fair value in the period (92) (54) $ (424)
Losses/(gains) reclassified from reserves to income statement (3,439) 655 $ (2,357)
Aluminium embedded derivatives separated from the power contract      
Disclosure of detailed information about financial instruments [line items]      
Nominal amount (US$ millions) 890 1,050  
Carrying amount (113) (174)  
Change in fair value in the period 42 3  
Embedded derivatives in other financial liabilities 113 174  
Highly probable forecast aluminum sales      
Disclosure of detailed information about financial instruments [line items]      
Cash flow hedge reserve (39) (91)  
Change in fair value in the period (26) (16)  
Highly probable forecast aluminum sales | Cash flow hedge reserve      
Disclosure of detailed information about financial instruments [line items]      
Total hedging gains/(losses) recognised in reserves 42 (1)  
Hedge ineffective-ness in the period (losses)/gains 0 4  
Losses/(gains) reclassified from reserves to income statement $ 5 $ (2)