Income Taxes (Parenthetical) (Detail) (CAD) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Income Tax [Line Items]
Cash outflow from income taxes, plus investment credits earned	911	871	667

Net cash outflow resulting from current and deferred income tax expenses, plus investment tax credits earned.

No definition available.

Name:	imo_CashOutflowFromIncomeTaxesPlusInvestmentTaxCredit
Namespace Prefix:	imo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration