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Summary of significant accounting policies - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2013 Y
Significant Accounting Policies [Line Items] |
Estimated service life of the asset refineries, in years | 25
Estimated service life of other major assets, in years | 20
Amortization of computer software development costs, in years | 15
Amortization of customer lists, in years | 10 years
Maximum |
Significant Accounting Policies [Line Items] |
Investments in mining and transportation systems at oil sands mining properties, useful life | 15 years
Syncrude Joint Venture |
Significant Accounting Policies [Line Items] |
Undivided interest in oil and gas activities | 25.00%
Kearl Project |
Significant Accounting Policies [Line Items] |
Undivided interest in oil and gas activities | 70.96%

X
- Definition Amortization of computer software development costs + References No definition available. + Details
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Namespace Prefix: | imo_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated service life of refineries + References No definition available. + Details
Name: | imo_EstimatedServiceLifeOfAssetRefineries
Namespace Prefix: | imo_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated service life of other major assets, including chemical plants and service stations. + References No definition available. + Details
Name: | imo_EstimatedServiceLifeOtherMajorAssets
Namespace Prefix: | imo_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | imo_SignificantAccountingPoliciesLineItems
Namespace Prefix: | imo_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Undivided interest in oil and gas activities conducted jointly with third parties. + References No definition available. + Details
Name: | imo_UndividedInterestInOilAndGasActivities
Namespace Prefix: | imo_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration