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Equity (Tables) | 3 Months Ended
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Mar. 31, 2018
Equity [Abstract] |
Schedule of Stockholders Equity [Table Text Block] | The changes in the number of units outstanding during the three months ended March 31, 2018 are summarized below:
(In units) | Common |  | General Partner |  | Total
Balance at December 31, 2017 | 407,130,020 |  |  | 8,308,773 |  |  | 415,438,793 |
Unit-based compensation awards(1) | 150,257 |  |  | 140 |  |  | 150,397 |
Contribution of refining logistics and fuels distribution assets(2) | 111,611,111 |  |  | 2,277,778 |  |  | 113,888,889 |
Conversion of GP economic interests | 275,000,000 |  |  | (10,586,691 | ) |  | 264,413,309 |
Balance at March 31, 2018 | 793,891,388 |  |  | — |  |  | 793,891,388 |
(1) | As a result of the unit-based compensation awards issued during the period, MPLX GP contributed less than $1 million in exchange for 140 general partner units to maintain its two percent GP Interest.
(2) | MPC agreed to waive approximately one-third of the first quarter 2018 distributions on the common units issued in connection with this transaction. As a result of this waiver, MPC will not receive $23.7 million of the distributions that would have otherwise accrued on such common units with respect to the first quarter 2018. See Note 4 for information regarding this acquisition.
Schedule Of Calculation Of Net Income Applicable to Partners [Table Text Block] | The following table presents the allocation of the general partner’s GP Interest in net income attributable to MPLX LP, for income statement periods occurring prior to the exchange of the GP economic interests:
| Three Months Ended March 31,
(In millions) | 2017
Net income attributable to MPLX LP | $ | 150 |
Less: Preferred unit distributions | 16 |
General partner's IDRs and other | 61 |
Net income attributable to MPLX LP available to general and limited partners | $ | 73 |
General partner's two percent GP Interest in net income attributable to MPLX LP | $ | 1 |
General partner's IDRs and other | 61 |
General partner's GP Interest in net income attributable to MPLX LP | $ | 62 |
Distributions Made to Limited Partner, by Distribution [Table Text Block] | The allocation of total quarterly cash distributions to general, limited and preferred unitholders is as follows for the three months ended March 31, 2018 and 2017. The Partnership’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned.
| Three Months Ended March 31,
(In millions) | 2018 |  | 2017
General partner's distributions: |  |  |
General partner's distributions on general partner units | $ | — |  |  | $ | 5 |
General partner's distributions on IDRs | — |  |  | 60 |
Total distribution on general partner units and IDRs | $ | — |  |  | $ | 65 |
Common and preferred unit distributions: |  |  |
Common unitholders, includes common units of general partner | $ | 467 |  |  | $ | 198 |
Preferred unit distributions | 16 |  |  | 16 |
Total cash distributions declared | $ | 483 |  |  | $ | 279 |

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- Definition Tabular disclosure of payment of cash or stock made to limited partner of limited partnership (LP). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 272 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 272 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055 + Details
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- Definition Tabular disclosure of changes in the separate accounts comprising stockholders' equity (in addition to retained earnings) and of the changes in the number of shares of equity securities during at least the most recent annual fiscal period and any subsequent interim period presented is required to make the financial statements sufficiently informative if both financial position and results of operations are presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 + Details
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