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Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Estimated service life of the asset refineries, in years	25 years
Estimated service life of other major assets, in years	20 years
Amortization of computer software development costs, in years	15 years
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%imo_UndividedInterestInOilAndGasActivities / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = imo_SyncrudeJointVentureMember
Kearl Joint Venture
Significant Accounting Policies [Line Items]
Undivided interest in oil and gas activities	70.96%imo_UndividedInterestInOilAndGasActivities / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = imo_KearlJointVentureMember

X

- Definition

Amortization of computer software development costs

+ References

No definition available.

+ Details

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Namespace Prefix:	imo_
Data Type:	xbrli:durationItemType
Balance Type:	na
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X

- Definition

Estimated service life of refineries

+ References

No definition available.

+ Details

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Namespace Prefix:	imo_
Data Type:	xbrli:durationItemType
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:durationItemType
Balance Type:	na
Period Type:	duration

X

- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
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X

- Definition

Undivided interest in oil and gas activities conducted jointly with third parties.

+ References

No definition available.

+ Details

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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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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- Details

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Namespace Prefix:
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X

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=imo_KearlJointVentureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Period Type: