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Accumulated Other Comprehensive Income | 3 Months Ended
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Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items] |
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] | Accumulated Other Comprehensive Loss MPLX LP records an accumulated other comprehensive loss on its Consolidated Balance Sheets relating to pension and other post-retirement benefits provided by the LOOP and Explorer joint-interests to their employees. MPLX LP is not a sponsor of these benefit plans. As a transfer between entities under common control, the Partnership recorded the Joint-Interest Acquisition from MPC on its Consolidated Balance Sheets at MPC’s historical basis, which included accumulated other comprehensive loss. MPLX LP’s assumption of the accumulated other comprehensive loss balance had no effect on MPLX LP’s comprehensive income during the period as the balance was accumulated while under the ownership of MPC. The following table shows the changes in accumulated other comprehensive loss by component during the period December 31, 2017 through March 31, 2018.
(In millions) | Pension Benefits |  | Other Post-Retirement Benefits |  | Total
Balance as of December 1, 2017(1) | $ | (13 | ) |  | $ | (1 | ) |  | $ | (14 | )
Other comprehensive loss - remeasurements(2) | (1 | ) |  | (1 | ) |  | (2 | )
Balance as of March 31, 2018(1) | $ | (14 | ) |  | $ | (2 | ) |  | $ | (16 | )
(1) | These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included in the Consolidated Statements of Income under the caption “Income (loss) from equity method investments.”
(2) | Components of “Other comprehensive loss - remeasurements” relate to actuarial gains and losses as well as amortization of prior service costs. The Partnership records an adjustment to comprehensive income in accordance with its ownership interest in LOOP and Explorer.

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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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- Definition The entire disclosure for comprehensive income, which includes, but is not limited to, 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -URI http://asc.fasb.org/topic&trid=2134417 + Details
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