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Decommissioning Liabilities - Additional Information (Detail) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Disclosure of other provisions [line items]    
Estimated future cash flows required to settle the obligation $ 14,000 $ 5,000
Credit-adjusted risk-free rate 4.40% 5.00%
Inflation Rate 2.00% 2.00%
Restricted Cash $ 186 $ 0
Bottom of range    
Disclosure of other provisions [line items]    
Expected settlement of decommissioning liabilities $ 230