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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
Derivative Instruments and Hedging Activities Disclosure [Abstract] |  |  |  |
Revenues | $ 20 | $ (34) | $ 11 | $ (47)

X
- Definition Total realized and unrealized revenue on derivative instrument. + References No definition available. + Details
Name: | imo_RealizedAndUnrealizedRevenueOnDerivativeInstrument
Namespace Prefix: | imo_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration