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Income Taxes - Additional Informations (Detail) - CAD ($)
$ in Millions
12 Months Ended
Aug. 01, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of income tax [line items]        
Transition tax related to US tax reform   $ 1.1 $ (10.0) $ 31.2
Revaluation due to US tax reform $ 10.0     $ 12.6
Federal tax rate   27.00% 27.10%  
United States [member]        
Disclosure of income tax [line items]        
Federal tax rate     21.00% 21.00%