Business Segments (Parenthetical) (Detail) - CAD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
United States Exports
Segment Reporting Information [Line Items]
Operating revenues	$ 1,569	$ 1,373

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