Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Actuarial changes, tax	$ 1	$ 6
Prior service credit, tax	(3)	(8)
Other, tax	$ 0	$ 0

Amount of tax (expense) benefit, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to net prior service cost (credit) pension and other postretirement defined benefit plans.

No definition available.

Name:	mpc_OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansNetPriorServiceCostCreditAdjustmentTax
Namespace Prefix:	mpc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration