Pension and other benefits - Narrative (Details) - CAD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Pensions
Defined Benefit Plan Disclosure [Line Items]
Contributions made by the Company	$ 3	$ 5	$ 11	$ 10

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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+ Details

- Definition

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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