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Other comprehensive income (loss) information - Income Tax Expense (Credit) for Components of Other Comprehensive Income (Loss) (Detail) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Equity [Abstract]
Postretirement benefits liability adjustment (excluding amortization)	$ 0	$ 1	$ 4	$ 1
Amortization of postretirement benefits liability adjustment included in net benefit cost	2	3	5	12
Total	$ 2	$ 4	$ 9	$ 13

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Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

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-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-SubTopic 10
-Topic 220
-Publisher FASB
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Amount, after reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income of defined benefit plan.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

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