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Income taxes - Narrative (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Income Taxes [Abstract]      
Applicable statutory tax rate 26.80% 26.80%  
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]      
Deferred tax asset $ (4,869) $ (4,574) $ (3,704)
Non-capital tax loss carryforwards      
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]      
Unused tax loss carryforward 251 266  
Deferred tax asset 60 63 $ 69
Unused tax losses for which no deferred tax asset recognised 20 17  
Non-capital Loss Carryforwards With Deferred Tax Asset      
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]      
Unused tax loss carryforward 231 249  
Capital loss carryforwards      
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]      
Unused tax loss carryforward $ 67 $ 69