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Significant Accounting Policies - Additional Information (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Jan. 01, 2019
Disclosure Of Significant Accounting Policies [Line Items]    
Cash and cash equivalents orginal maturity three months or less  
Events After Reporting Period [Member]    
Disclosure Of Significant Accounting Policies [Line Items]    
Lease liabilities   $ 60
Right-of-use assets   $ 70
Top of Range [Member] | Software [Member]    
Disclosure Of Significant Accounting Policies [Line Items]    
Expected useful life of intangible asset 10 years