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MPLX LP (Detail) - MPLX LP | Mar. 31, 2018
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Noncontrolling Interest [Line Items] |
Ownership percentage of general partner interest | 100.00%
Public's ownership interest in MPLX (in percentage) | 36.40%
General Partner and Limited Partner |
Noncontrolling Interest [Line Items] |
MPC's partnership interest in MPLX (in percentage) | 63.60%

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- Definition Percentage ownership of the general partner interest + References No definition available. + Details
Name: | mpc_OwnershipPercentageOfGeneralPartnerInterest
Namespace Prefix: | mpc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | dei_LegalEntityAxis=mpc_MPLXLPMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=mpc_GeneralPartnerAndLimitedPartnerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |