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MPLX LP (Detail) - MPLX LP	Mar. 31, 2018
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%

X

- Definition

Percentage ownership of the general partner interest

+ References

No definition available.

+ Details

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Namespace Prefix:	mpc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- 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

Name:	us-gaap_MinorityInterestLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
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

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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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:
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