Income taxes - Reconciliation of Uncertain Tax Positions Related to Unrecognized Tax Benefits (Details) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of Uncertain Tax Positions to Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits at January 1	$ 22	$ 20	$ 49
Tax benefits related to the current year	1	2	1
Tax benefits related to prior years	14	10	0
Tax benefits acquired with KCS	0	2	0
Gross uncertain tax benefits related to prior years	(1)	(6)	(30)
Settlements with taxing authorities	(7)	(6)	0
Unrecognized tax benefits at December 31	$ 29	$ 22	$ 20

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

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- Definition

Amount of increase in unrecognized tax benefits resulting from acquisitions.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of increase in unrecognized tax benefits resulting from settlements with taxing authorities.

+ References

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