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Other Long-Term Obligations (Parenthetical) (Detail) - CAD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Schedule of Other Liabilities [Line Items]    
Employee retirement benefit obligations in current liabilities $ 58 $ 55
Asset retirement obligations and other environmental liabilities in current liabilities $ 124 $ 118
Asset retirement obligations discount rate 6.00% 6.00%