v3.3.0.814

Related Party Agreements and Transactions - Summary of Deferred Revenue - Related Parties (Detail) - MPC [Member] - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	$ 38.9	$ 34.5
Minimum volume deficiencies [Member]
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	33.7	29.9
Project Reimbursements [Member]
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	$ 5.2	$ 4.6

X

- Definition

Deferred revenue with related parties, including both current and non current portions.

+ References

No definition available.

+ Details

Name:	mplx_DeferredRevenueRelatedParties
Namespace Prefix:	mplx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=mplx_MarathonPetroleumCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DeferredRevenueArrangementTypeAxis=mplx_MinimumCommittedVolumeContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DeferredRevenueArrangementTypeAxis=mplx_ReimbursableProjectsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: