Transaction With related Parties - Additional Information (Detail) (CAD) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Long-Term Loans
Related Party Transaction [Line Items]
Outstanding loans from an affiliate	4,316	1,040
Short-Term Loans
Related Party Transaction [Line Items]
Outstanding loans from an affiliate	75

Outstanding loans from an affiliate, includes both current and noncurrent portion.

No definition available.

Name:	imo_OutstandingLoansFromAffiliate
Namespace Prefix:	imo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant