Other long-term obligations - Table Narrative (Detail) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Other Liabilities Disclosure [Abstract]
Employee retirement benefit obligations in current liabilities	$ 63	$ 61
Asset retirement obligations and other environmental liabilities in current liabilities	$ 318	$ 291
Asset retirement obligations discount rate	6.00%	6.00%

Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as current.

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