Business Segments (Parenthetical) (Detail) - CAD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
United States Exports
Segment Reporting Information [Line Items]
Operating revenues	$ 739	$ 2,152	$ 2,112	$ 3,816

Total revenue from sales of goods and services during the reporting period, reduced by sales returns and allowances and sales discounts. Also includes federal excise tax which is then deducted as an expense.

No definition available.

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