Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Actuarial changes, tax	$ 24	$ 2	$ 29	$ 9
Prior service costs, tax	(3)	(4)	(7)	(12)
Other, tax	$ (1)	$ 0	$ (2)	$ 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