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Income Taxes - Contingencies (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Maximum    
Disclosure of contingent liabilities [line items]    
Tax expense, reassessed tax liability $ 57  
Minimum    
Disclosure of contingent liabilities [line items]    
Tax expense, reassessed tax liability 0  
Uncertain tax positions    
Disclosure of contingent liabilities [line items]    
Provision for uncertain tax positions $ 0 $ 0