Income taxes (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Business Acquisition [Line Items]
Effective tax rate	16.90%	12.67%
Effective tax rate, excluding discrete items	24.50%	24.25%
Equity earnings of Kansas City Southern	$ (204)	$ (198)
Outside basis deferred tax recovery	23	32
KCS
Business Acquisition [Line Items]
Acquisition-related costs	15	20
KCS | Purchased services and other
Business Acquisition [Line Items]
Acquisition-related costs	$ 12	$ 20