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Equity-Based Compensation Plan (Tables) | 3 Months Ended
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Mar. 31, 2018
Phantom Units |
Equity Transactions And Share Based Compensation [Line Items] |
Summary of Share-based Compensation, Restricted Stock Units Award Activity | The following is a summary of phantom unit award activity of MPLX LP common units for the three months ended March 31, 2018:
| Number of Units |  | Weighted Average Fair Value
Outstanding at December 31, 2017 | 1,351,523 |  |  | $ | 34.53 |
Granted | 169,310 |  |  | 35.00 |
Settled | (217,093 | ) |  | 33.83 |
Forfeited | (46,330 | ) |  | 34.95 |
Outstanding at March 31, 2018 | 1,257,410 |  |  | 34.70 |
Performance Shares [Member] |
Equity Transactions And Share Based Compensation [Line Items] |
Summary of Share-based Compensation, Restricted Stock Units Award Activity | The following is a summary of the activity for performance unit awards to be settled in MPLX LP common units for the three months ended March 31, 2018:
| Number of Units
Outstanding at December 31, 2017 | 2,536,594 |
Granted | — |
Settled | (538,594 | )
Forfeited | (50,000 | )
Outstanding at March 31, 2018 | 1,948,000 |

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- Definition Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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