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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

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- Definition Book Value of Assets Sold + References No definition available. + Details
Name: | imo_BookValueOfAssetsSold
Namespace Prefix: | imo_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Net gain (loss) on asset sales, after tax. + References No definition available. + Details
Name: | imo_NetGainLossOnAssetSalesAfterTax
Namespace Prefix: | imo_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
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Data Type: | xbrli:stringItemType
Balance Type: | na
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- Definition Aggregate cash proceeds received from a combination of transactions that are classified as investing activities in which assets, which may include one or more investments, are sold to third-party buyers. This element can be used by entities to aggregate proceeds from all asset sales that are classified as investing activities. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name Accounting Standards Codification -Section 45 -Paragraph 12 -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-12 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration