Pensions and other benefits - Amounts Recognized in Company's Consolidated Balance Sheets (Details) - CAD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Pension asset	$ 3,101	$ 2,317
Pension and other benefit liabilities	(538)	(718)
Pensions
Defined Benefit Plan Disclosure [Line Items]
Pension asset	3,101	2,317
Accounts payable and accrued liabilities	(10)	(11)
Pension and other benefit liabilities	(165)	(252)
Total amount recognized	2,926	2,054
Other benefits
Defined Benefit Plan Disclosure [Line Items]
Pension asset	0	0
Accounts payable and accrued liabilities	(33)	(32)
Pension and other benefit liabilities	(373)	(466)
Total amount recognized	$ (406)	$ (498)