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Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income | 12 Months Ended
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Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items] |
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] | Accumulated Other Comprehensive Loss MPLX records an accumulated other comprehensive loss on the Consolidated Balance Sheets relating to pension and other post-retirement benefits provided by LOOP and Explorer to their employees. MPLX is not a sponsor of these benefit plans. As a transfer between entities under common control, MPLX recorded the Joint-Interest Acquisition from MPC on the Consolidated Balance Sheets at MPC’s historical basis, which included accumulated other comprehensive loss. MPLX’s assumption of the accumulated other comprehensive loss balance had no effect on MPLX’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, 2016 through December 31, 2018:
(In millions) | Pension Benefits |  | Other Post-Retirement Benefits |  | Total
Balance at December 31, 2016 | $ | — |  |  | $ | — |  |  | $ | — |
Joint-Interest Acquisition | (13 | ) |  | (1 | ) |  | (14 | )
Balance at December 31, 2017(1) | (13 | ) |  | (1 | ) |  | (14 | )
Other comprehensive loss - remeasurements(2) | (1 | ) |  | (1 | ) |  | (2 | )
Balance as of December 31, 2018(1) | $ | (14 | ) |  | $ | (2 | ) |  | $ | (16 | )
(1) | These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on 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. MPLX 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 Tabular disclosure of components of comprehensive income (loss). Includes, but is not limited to, foreign currency translation adjustments, foreign currency transactions designated as economic hedges of a net investment in foreign entity, gain (loss) and prior service cost (credit) for pension plans and other postretirement benefit plans. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e526-108580 + Details
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