Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Actuarial changes, tax	$ (1)	$ 34	$ 0	$ 169
Prior service costs, tax	$ (5)	$ (5)	$ (14)	$ (14)

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