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Financial Instruments - Additional Information (Detail) - CAD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Disclosure of detailed information about financial instruments [Line Items]    
Fair value of unsecured senior notes $ 1,428 $ 1,548
Credit Risk [Member]    
Disclosure of detailed information about financial instruments [Line Items]    
Trade receivables $ 12 $ 18