Pension and other benefits - Narrative (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pensions
Defined Benefit Plan Disclosure [Line Items]
Contributions made by the Company	$ 4	$ 5	$ 13	$ 12