Income taxes (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Business Acquisition [Line Items]
Effective tax rate	25.09%	16.90%
Effective tax rate, excluding discrete items	25.00%	24.50%
Equity earnings of Kansas City Southern	$ 0	$ 204
Outside basis deferred tax recovery		23
Mexican Tax Authority
Business Acquisition [Line Items]
Other tax expense (benefit)	10
KCS
Business Acquisition [Line Items]
Amortization of fair value adjustments	84
Acquisition-related costs	$ 26	$ 15