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Financial Instruments - Summary of Urealized Risk Management Positions (Detail) - CAD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure Of Recurring Fair Value Measurement Of Assets And Liabilities [Line Items]      
Risk Management Net Asset (Liability) $ (68) $ (53) $ 3
Level 2 of fair value hierarchy      
Disclosure Of Recurring Fair Value Measurement Of Assets And Liabilities [Line Items]      
Risk Management Net Asset (Liability) (68) (53)  
Level 2 of fair value hierarchy | Commodity price risk      
Disclosure Of Recurring Fair Value Measurement Of Assets And Liabilities [Line Items]      
Risk Management Asset 48 5  
Risk Management Liability 116 58  
Risk Management Net Asset (Liability) (68) (53)  
Level 2 of fair value hierarchy | Commodity price risk | Crude Oil, Natural Gas, Condensate and Refined Products      
Disclosure Of Recurring Fair Value Measurement Of Assets And Liabilities [Line Items]      
Risk Management Asset 46 5  
Risk Management Liability 116 58  
Risk Management Net Asset (Liability) (70) (53)  
Level 2 of fair value hierarchy | Commodity price risk | Exchange Rate Contracts      
Disclosure Of Recurring Fair Value Measurement Of Assets And Liabilities [Line Items]      
Risk Management Asset 2 0  
Risk Management Liability 0 0  
Risk Management Net Asset (Liability) $ 2 $ 0