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v3.19.3.a.u2

Litigation and Other Contingencies - Additional Information (Detail) - CAD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018
Litigation And Other Contingencies [Line Items] |  |
Total payment on unconditional purchase obligation | $ 0 |
Total other third party obligations payable | 30 | $ 35
Indemnification Agreement [Member] |  |
Litigation And Other Contingencies [Line Items] |  |
Total other third party obligations payable | $ 64 | $ 46

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- Definition Litigation And Other Contingencies [Line Items] + References No definition available. + Details
Name: | imo_LitigationAndOtherContingenciesLineItems
Namespace Prefix: | imo_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The minimum amount the entity agreed to spend under the long-term purchase commitment. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions. + References No definition available. + Details
Name: | us-gaap_OtherCommitment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_IndemnificationGuaranteeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |