Shareholders' equity - Narrative (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Preferred shares issued	0
Share capital
Class of Stock [Line Items]
Stock-based compensation transferred from APIC	$ 18	$ 17	$ 9