Stock-based compensation - Summary of Total Share Based Liabilities (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	$ 89	$ 137	$ 126
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	86	116	119
DSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	2	16	1
Other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	$ 1	$ 5	$ 6