Pension and other benefits - Narrative (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pensions
Defined Benefit Plan Disclosure [Line Items]
Contributions made by the Company	$ 5	$ 4	$ 9	$ 7