Stock-based compensation (Expense and Tax Benefits) (Details) - CAD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Share-based Payment Arrangement, Additional Disclosure [Abstract] | |||
| Total stock-based compensation expense | $ 106 | $ 74 | $ 64 |
| Tax benefit recognized in income | 27 | 18 | 15 |
| Excess tax benefit (deficiency) recognized in income | (6) | 15 | 10 |
| Stock Option Plan | |||
| Share-based Payment Arrangement, Additional Disclosure [Abstract] | |||
| Total stock-based compensation expense | 11 | 12 | 11 |
| Employee Share Investment Plan | |||
| Share-based Payment Arrangement, Additional Disclosure [Abstract] | |||
| Total stock-based compensation expense | 30 | 28 | 26 |
| Share Units Plan | |||
| Share-based Payment Arrangement, Additional Disclosure [Abstract] | |||
| Total stock-based compensation expense | 64 | 33 | 25 |
| Voluntary Incentive Deferral Plan (VIDP) | |||
| Share-based Payment Arrangement, Additional Disclosure [Abstract] | |||
| Total stock-based compensation expense | $ 1 | $ 1 | $ 2 |