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Common Shares - Additional Information (Detail) (CAD)
In Millions, except Share data, unless otherwise specified
12 Months Ended 228 Months Ended
Dec. 31, 2014
Dec. 31, 2012
Dec. 31, 2014
Class of Stock [Line Items]      
Normal course issuer bid share repurchase shares authorized 1,000,000us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased   1,000,000us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased
Normal course issuer bid share repurchase programs 19imo_NormalCourseIssuerBidShareRepurchasePrograms   19imo_NormalCourseIssuerBidShareRepurchasePrograms
Normal course issuer bid share repurchase term, months 12 months    
Exxon Mobil Corporation's ownership interest in Imperial 69.60%imo_MajorityInterestOwnershipPercentage   69.60%imo_MajorityInterestOwnershipPercentage
Cumulative purchases to date, shares 2,000us-gaap_StockRepurchasedAndRetiredDuringPeriodShares 2,776,000us-gaap_StockRepurchasedAndRetiredDuringPeriodShares 906,543,000us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Cumulative purchases to date, value     15,708us-gaap_StockRepurchasedAndRetiredDuringPeriodValue