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Period End Capitalized Suspended Exploratory Well Costs (Detail) (CAD) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items] |  |  |
Capitalized suspended exploratory well costs, total | 167 us-gaap_CapitalizedExploratoryWellCosts | 173 us-gaap_CapitalizedExploratoryWellCosts | 167 us-gaap_CapitalizedExploratoryWellCosts
Beginning Balance | 173 us-gaap_CapitalizedExploratoryWellCosts | 167 us-gaap_CapitalizedExploratoryWellCosts | 163 us-gaap_CapitalizedExploratoryWellCosts
Additions pending the determination of proved reserves | 5 us-gaap_CapitalizedExploratoryWellCostAdditionsPendingDeterminationOfProvedReserves | 12 us-gaap_CapitalizedExploratoryWellCostAdditionsPendingDeterminationOfProvedReserves | 16 us-gaap_CapitalizedExploratoryWellCostAdditionsPendingDeterminationOfProvedReserves
Charged to expense |  |  |
Reclassification to wells, facilities and equipment based on the determination of proved reserves | (11)us-gaap_ReclassificationToWellFacilitiesAndEquipmentBasedOnDeterminationOfProvedReserves | (6)us-gaap_ReclassificationToWellFacilitiesAndEquipmentBasedOnDeterminationOfProvedReserves | (12)us-gaap_ReclassificationToWellFacilitiesAndEquipmentBasedOnDeterminationOfProvedReserves
Ending Balance | 167 us-gaap_CapitalizedExploratoryWellCosts | 173 us-gaap_CapitalizedExploratoryWellCosts | 167 us-gaap_CapitalizedExploratoryWellCosts
Capitalized for a period of one year or less |  | 6 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodOfOneYearOrLess | 16 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodOfOneYearOrLess
Capitalized For A Period Of Between One And Five Years |  |  |
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items] |  |  |
Capitalized suspended exploratory well costs | 167 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfBetweenOneAndFiveYearsMember | 167 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfBetweenOneAndFiveYearsMember | 151 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfBetweenOneAndFiveYearsMember
Capitalized For A Period Of Greater Than One Year |  |  |
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items] |  |  |
Capitalized suspended exploratory well costs | 167 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfGreaterThanOneYearMember | 167 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfGreaterThanOneYearMember | 151 us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfGreaterThanOneYearMember

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- Definition Additions to capitalized exploratory well costs that were added during the reporting period pending the determination of proved reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447 + Details
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- Definition Capitalized exploratory well costs that were expensed during the year because proved reserves were not found at the exploratory well. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447 + Details
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- Definition The amount of capitalized exploratory well costs that is pending the determination of proved reserves. This does not include amounts that were capitalized and subsequently expensed in the same annual period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447 + Details
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- Definition The amount of exploratory well costs that have been capitalized for a period of greater than one year after the completion of drilling. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph b -URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447 + Details
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- Definition The amount of exploratory well costs that have been capitalized for a period of one year or less after the completion of drilling. + References No definition available. + Details
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- Definition Previously capitalized costs of the drilling of wells that were reclassified as part of the costs of the enterprise's wells and related equipment and facilities at the time that proved reserves were found. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447 + Details
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