Other Comprehensive Income Information (Amounts Reclassified Out Of Acc Other Comp Income) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Other Comprehensive Income Information Before Tax [Abstract]
Amortization and settlement of postretirement benefits reserves adjustment included in net periodic benefit costs (Statement of Income line: Non-service pension and postretirement benefit expense)	$ (262)	$ (237)

Defined Benefit Plan Amortization Of Actuarial Loss/Gain And Prior Service Cost Credit And Recognized Net Gain/Loss Due To Settlements And Curtailments

No definition available.

Name:	xom_DefinedBenefitPlanAmortizationOfActuarialLossGainAndPriorServiceCostCreditAndRecognizedNetGainLossDueToSettlementsAndCurtailments
Namespace Prefix:	xom_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration