Pensions and other benefits - Amounts Recognized in Accumulated Other Comprehensive Losses (Details) - CAD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Pensions
Defined Benefit Plan Disclosure [Line Items]
Other than deferred investment (losses) gains	$ (1,711)	$ (3,298)
Deferred investment (losses) gains	(301)	672
Prior service cost	(31)	(5)
Deferred income tax	608	759
Total	(1,435)	(1,872)
Other benefits
Defined Benefit Plan Disclosure [Line Items]
Other than deferred investment (losses) gains	35	(57)
Deferred investment (losses) gains	0	0
Prior service cost	(1)	(1)
Deferred income tax	(9)	15
Total	$ 25	$ (43)