XML 473 R161.htm IDEA: XBRL DOCUMENT v3.23.1
Financial instruments and risk management - Summary of changes in market price relevant to alumina purchase price swaps outstanding (Detail) - Commodity price risk - Aluminium - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Disclosure of detailed information about financial instruments [line items]    
Percentage increase in market price change 10.00%  
Percentage decrease in market price change (10.00%)  
Increase in market prices, effect on net earnings $ (78) $ (19)
Decrease in market prices, effect on net earnings 73 19
Increase in market prices, effect on equity (98) (98)
Decrease in market prices, effect on equity $ 95 $ 100