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Supplemental Cash Flow Information - Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures (Detail) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Supplemental Cash Flow Elements [Abstract] |  |
(Decrease) increase in capital accruals | $ (6) | $ 2

X
- Definition Increase (Decrease) In Capital Accruals + References No definition available. + Details
Name: | mpc_IncreaseDecreaseInCapitalAccruals
Namespace Prefix: | mpc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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