Employee retirement benefits - Components of Net Periodic Benefit Cost (Detail) - CAD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
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| Pension benefits: | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | $ 43 | $ 46 | $ 130 | $ 139 |
| Interest cost | 94 | 93 | 284 | 277 |
| Expected return on plan assets | (101) | (99) | (302) | (296) |
| Amortization of prior service cost (credit) | 9 | 7 | 22 | 21 |
| Amortization of actuarial loss (gain) | (1) | 2 | (1) | 8 |
| Net other postretirement benefits enhancement and curtailment cost | 0 | 19 | 0 | 19 |
| Net benefit cost | 44 | 68 | 133 | 168 |
| Other postretirement benefits: | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | 0 | 2 | 2 | 4 |
| Interest cost | 7 | 4 | 18 | 15 |
| Amortization of prior service cost (credit) | (2) | (1) | (4) | (3) |
| Amortization of actuarial loss (gain) | (2) | (1) | (7) | (6) |
| Net other postretirement benefits enhancement and curtailment cost | (6) | 1 | (7) | 1 |
| Net benefit cost | $ (3) | $ 5 | $ 2 | $ 11 |
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- 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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of cost recognized for passage of time related to defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of defined benefit plan cost (credit), classified as other. No definition available.
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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