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Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018
Statement of Comprehensive Income [Abstract] |  |  |  |
Actuarial changes, tax | $ (14) | $ 24 | $ (8) | $ 29
Prior service credit, tax | (3) | (3) | (14) | (7)
Other, tax | $ 0 | $ (1) | $ (1) | $ (2)

X
- Definition 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. + References No definition available. + Details
Name: | mpc_OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansNetPriorServiceCostCreditAdjustmentTax
Namespace Prefix: | mpc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of tax expense (benefit), after reclassification adjustments, of increase (decrease) in accumulated other comprehensive income (loss) related to the net actuarial gain (loss) pension and other postretirement defined benefit plans. + References No definition available. + Details
Name: | mpc_OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansNetUnamortizedGainLossAdjustmentTax
Namespace Prefix: | mpc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Other Comprehensive Income, Other, Tax + References No definition available. + Details
Name: | mpc_OtherComprehensiveIncomeOtherTax
Namespace Prefix: | mpc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration