Investment and other income - Gains and Losses on Asset Sales (Detail) - CAD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2025 |
Sep. 30, 2024 |
Sep. 30, 2025 |
Sep. 30, 2024 |
|
| Other Income and Expenses [Abstract] | ||||
| Proceeds from asset sales | $ 21 | $ 0 | $ 34 | $ 7 |
| Book value of asset sales | 43 | (2) | 45 | 2 |
| Gain (loss) on asset sales, before-tax | (22) | 2 | (11) | 5 |
| Gain (loss) on asset sales, after-tax | $ (24) | $ 2 | $ (14) | $ 5 |