Stock-based compensation - Summary of Total Share Based Liabilities (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	$ 64	$ 89	$ 137
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	54	86	116
DSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	9	2	16
Other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based liabilities paid	$ 1	$ 1	$ 5