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Financial instruments and risk management - Gains or losses associated with ten percent strengthening of US Dollar (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Disclosure of detailed information about hedging instruments [Line Items]      
Effect on net earnings $ (14) $ (300) $ 52
Australian dollar      
Disclosure of detailed information about hedging instruments [Line Items]      
Closing exchange rate 0.73 0.77 0.70
Canadian dollar      
Disclosure of detailed information about hedging instruments [Line Items]      
Closing exchange rate 0.78 0.78 0.77
Foreign exchange risk | Australian dollar      
Disclosure of detailed information about hedging instruments [Line Items]      
Closing exchange rate 73 77  
Effect on net earnings $ 379 $ 625  
Amount impacting underlying earnings (18) (11)  
Impact directly on equity $ (1,044) $ (1,105)  
Foreign exchange risk | Canadian dollar      
Disclosure of detailed information about hedging instruments [Line Items]      
Closing exchange rate 78 78  
Effect on net earnings $ (111) $ (167)  
Amount impacting underlying earnings (3) 6  
Impact directly on equity $ 0 $ 0