Income taxes (Details) - CAD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Business Acquisition [Line Items]
Effective tax rate	24.32%	25.09%
Effective tax rate, excluding discrete items	24.50%	25.00%
Settlement of Mexican tax audits	$ 11	$ 0
Mexican Tax Authority
Business Acquisition [Line Items]
Other tax expense (recovery)		10
Settlement of Mexican tax audits	11
KCS
Business Acquisition [Line Items]
Amortization of fair value adjustments	94	86
Acquisition-related costs	$ 20	$ 26

Business Combination, Amortization of Fair Value Adjustments

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Effective Income Tax Rate Reconciliation, Estimated Rate, Excluding Discrete Items, Percent

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Payments For Tax Settlement

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of other income tax expense (benefit).

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