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v3.10.0.1

Supplemental Cash Flow Information (Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract] |  |  |
Increase/(decrease) in capital accruals | $ 104 | $ 71 | $ (22)

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

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