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Period End Capitalized Suspended Exploratory Well Costs (Detail) (CAD) In Millions, unless otherwise specified	12 Months Ended
	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	167us-gaap_CapitalizedExploratoryWellCosts	173us-gaap_CapitalizedExploratoryWellCosts	167us-gaap_CapitalizedExploratoryWellCosts
Beginning Balance	173us-gaap_CapitalizedExploratoryWellCosts	167us-gaap_CapitalizedExploratoryWellCosts	163us-gaap_CapitalizedExploratoryWellCosts
Additions pending the determination of proved reserves	5us-gaap_CapitalizedExploratoryWellCostAdditionsPendingDeterminationOfProvedReserves	12us-gaap_CapitalizedExploratoryWellCostAdditionsPendingDeterminationOfProvedReserves	16us-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	167us-gaap_CapitalizedExploratoryWellCosts	173us-gaap_CapitalizedExploratoryWellCosts	167us-gaap_CapitalizedExploratoryWellCosts
Capitalized for a period of one year or less		6us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodOfOneYearOrLess	16us-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	167us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfBetweenOneAndFiveYearsMember	167us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfBetweenOneAndFiveYearsMember	151us-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	167us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfGreaterThanOneYearMember	167us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfGreaterThanOneYearMember	151us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear / imo_CapitalizedPeriodAxis = imo_CapitalizedForPeriodOfGreaterThanOneYearMember

X

- 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

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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

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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

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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

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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.

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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

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