Stock-based compensation - Summary of Total Share Based Liabilities (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	$ 126	$ 86	$ 58
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	119	76	54
DSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	1	9	4
Other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	$ 6	$ 1	$ 0