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Fair Value Measurements - Summary of Fair Values of Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - CAD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Jan. 01, 2017
Disclosure of fair value measurement of liabilities [line items]      
Settlement payables $ 45 $ 39 $ 43
Recurring Fair Value Measurement [member]      
Disclosure of fair value measurement of liabilities [line items]      
Derivative instruments and embedded derivatives 45 43  
Settlement payables 45 39  
Financial liabilities 90 82  
Level 2 [member] | Recurring Fair Value Measurement [member]      
Disclosure of fair value measurement of liabilities [line items]      
Derivative instruments and embedded derivatives 45 43  
Settlement payables 45 39  
Financial liabilities $ 90 $ 82