Financial and derivative instruments - Summary of realized and unrealized gain or (loss) on derivative instruments (Detail) - CAD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2025 |
Sep. 30, 2024 |
Sep. 30, 2025 |
Sep. 30, 2024 |
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| Derivative Instruments and Hedging Activities Disclosure [Abstract] | ||||
| Revenues | $ 20 | $ (34) | $ 11 | $ (47) |