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Net Income Per Limited Partner Unit (Tables) | 3 Months Ended
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Mar. 31, 2018
Earnings Per Share [Abstract] |
Schedule of Distributions By Partner By Class | For the three months ended March 31, 2018, the Partnership had dilutive potential common units consisting of certain equity-based compensation awards. For the three months ended March 31, 2017, the Partnership had dilutive potential common units consisting of certain equity-based compensation awards and Class B units. Potential common units omitted from the diluted earnings per unit calculation for the three months ended March 31, 2018 and March 31, 2017 were less than 1 million.
| Three Months Ended March 31,
(In millions) | 2018 |  | 2017
Net income attributable to MPLX LP | $ | 421 |  |  | $ | 150 |
Less: Limited partners’ distributions declared on Preferred units(1) | 16 |  |  | 16 |
General partner’s distributions declared (including IDRs)(1) | — |  |  | 65 |
Limited partners’ distributions declared on common units (including common units of general partner)(1) | 467 |  |  | 198 |
Undistributed net loss attributable to MPLX LP | $ | (62 | ) |  | $ | (129 | )
(1) | See Note 8 for distribution information.
Schedule of Basic and Diluted Earnings Per Unit |
| Three Months Ended March 31, 2018
(In millions, except per unit data) | Limited Partners’ Common Units |  | Redeemable Preferred Units |  | Total
Basic and diluted net income attributable to MPLX LP per unit: |  |  |  |  |
Net income attributable to MPLX LP: |  |  |  |  |
Distributions declared | $ | 467 |  |  | $ | 16 |  |  | $ | 483 |
Undistributed net loss attributable to MPLX LP | (62 | ) |  | — |  |  | (62 | )
Net income attributable to MPLX LP(1) | $ | 405 |  |  | $ | 16 |  |  | $ | 421 |
Weighted average units outstanding: |  |  |  |  |
Basic | 661 |  |  | 31 |  |  | 692 |
Diluted | 661 |  |  | 31 |  |  | 692 |
Net income attributable to MPLX LP per limited partner unit: |  |  |  |  |
Basic | $ | 0.61 |  |  |  |  |
Diluted | $ | 0.61 |  |  |  |  |
| Three Months Ended March 31, 2017
(In millions, except per unit data) | General Partner |  | Limited Partners’ Common Units |  | Redeemable Preferred Units |  | Total
Basic and diluted net income attributable to MPLX LP per unit: |  |  |  |  |  |  |
Net income attributable to MPLX LP: |  |  |  |  |  |  |
Distributions declared (including IDRs) | $ | 65 |  |  | $ | 198 |  |  | $ | 16 |  |  | $ | 279 |
Undistributed net loss attributable to MPLX LP | (3 | ) |  | (126 | ) |  | — |  |  | (129 | )
Net income attributable to MPLX LP(1) | $ | 62 |  |  | $ | 72 |  |  | $ | 16 |  |  | $ | 150 |
Weighted average units outstanding: |  |  |  |  |  |  |
Basic | 7 |  |  | 362 |  |  | 31 |  |  | 400 |
Diluted | 7 |  |  | 367 |  |  | 31 |  |  | 405 |
Net income attributable to MPLX LP per limited partner unit: |  |  |  |  |  |  |
Basic |  |  | $ | 0.20 |  |  |  |  |  |
Diluted |  |  | $ | 0.19 |  |  |  |  |  |
(1) | Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.

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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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