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Other Long-Term Obligations (Parenthetical) (Detail) - CAD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2022
Dec. 31, 2021
Schedule of Other Liabilities [Line Items]    
Employee retirement benefit obligations in current liabilities $ 56 $ 56
Asset retirement obligations and other environmental liabilities in current liabilities 102 102
Undiscounted Commitments 0 5
Accounts Payable and Accrued Liabilities [Member]    
Schedule of Other Liabilities [Line Items]    
Lease liability due within one year, Operating leases $ 95 $ 102