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Inventories - Additional Information (Detail) - CAD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2021
Dec. 31, 2020
Disclosure of inventories [line items]      
Cost of inventories recognized as expense during period   $ 34,000 $ 10,000
Inventory write-downs   $ 16  
Realized inventory write-down     547
Crude Oil Blend, Condensate and Refined Product Inventory      
Disclosure of inventories [line items]      
Inventory write-downs $ 588    
Reversed inventory write downs     39
Refined product      
Disclosure of inventories [line items]      
Inventory write-downs     $ 6