Pensions and other benefits - Amounts Recognized in Company's Consolidated Balance Sheets (Details) - CAD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Pension asset	$ 4,586	$ 3,338
Accounts payable and accrued liabilities	(45)	(48)
Pension and other benefit liabilities	(548)	(581)
Total amount recognized	3,993	2,709
Pensions
Defined Benefit Plan Disclosure [Line Items]
Pension asset	4,586	3,338
Accounts payable and accrued liabilities	(10)	(11)
Pension and other benefit liabilities	(150)	(161)
Total amount recognized	4,426	3,166
Other benefits
Defined Benefit Plan Disclosure [Line Items]
Pension asset	0	0
Accounts payable and accrued liabilities	(35)	(37)
Pension and other benefit liabilities	(398)	(420)
Total amount recognized	$ (433)	$ (457)