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Equity (Tables) | 12 Months Ended
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Dec. 31, 2018
Equity [Abstract] |
Schedule of Stockholders Equity | The table below summarizes the changes in the number of units outstanding for the years ended December 31, 2016, 2017, and 2018:
(In units) | Common |  | Class B |  | General Partner(1) |  | Total
Balance at December 31, 2015 | 296,687,176 |  |  | 7,981,756 |  |  | 6,800,475 |  |  | 311,469,407 |
Unit-based compensation awards | 120,989 |  |  | — |  |  | 2,470 |  |  | 123,459 |
Issuance of units under the ATM Program | 26,347,887 |  |  | — |  |  | 537,710 |  |  | 26,885,597 |
Contribution of HSM (See Note 4) | 22,534,002 |  |  | — |  |  | 459,878 |  |  | 22,993,880 |
Class B Conversion | 4,350,057 |  |  | (3,990,878 | ) |  | 7,330 |  |  | 366,509 |
Class A Reorganization | 7,153,177 |  |  | — |  |  | (436,758 | ) |  | 6,716,419 |
Balance at December 31, 2016 | 357,193,288 |  |  | 3,990,878 |  |  | 7,371,105 |  |  | 368,555,271 |
Unit-based compensation awards | 268,167 |  |  | — |  |  | 5,472 |  |  | 273,639 |
Issuance of units under the ATM Program | 13,846,998 |  |  | — |  |  | 282,591 |  |  | 14,129,589 |
Contribution of HST/WHC/MPLXT (See Note 4) | 12,960,376 |  |  | — |  |  | 264,497 |  |  | 13,224,873 |
Contribution of the Joint-Interest Acquisition (See Note 4) | 18,511,134 |  |  | — |  |  | 377,778 |  |  | 18,888,912 |
Class B conversion | 4,350,057 |  |  | (3,990,878 | ) |  | 7,330 |  |  | 366,509 |
Balance at December 31, 2017 | 407,130,020 |  |  | — |  |  | 8,308,773 |  |  | 415,438,793 |
Unit-based compensation awards | 348,387 |  |  | — |  |  | 140 |  |  | 348,527 |
Contribution of Refining Logistics and Fuels Distribution (See Note 4) | 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 December 31, 2018 | 794,089,518 |  |  | — |  |  | — |  |  | 794,089,518 |
(1) | Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest.
Schedule Of Calculation Of Net Income Applicable to Partners | Net Income Allocation – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to preferred unitholders first and subsequently allocated to the limited partner unitholders in accordance with their respective ownership percentages. Prior to 2018, when distributions related to the IDRs were made, earnings equal to the amount of those distributions were first allocated to the general partner before the remaining earnings are allocated to the unitholders, based on their respective ownership percentages. 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:
(In millions) | 2017 |  | 2016
Net income attributable to MPLX LP | $ | 794 |  |  | $ | 233 |
Less: Preferred unit distributions | 65 |  |  | 41 |
General partner's IDRs and other | 310 |  |  | 191 |
Net income attributable to MPLX LP available to general and limited partners | 419 |  |  | 1 |
General partner's two percent GP Interest in net income attributable to MPLX LP | 8 |  |  | — |
General partner's IDRs and other | 310 |  |  | 191 |
General partner's GP Interest in net income attributable to MPLX LP | $ | 318 |  |  | $ | 191 |
Distributions Made to Limited Partner, by Distribution | The allocation of total quarterly cash distributions to general, limited, and preferred unitholders is as follows for the years ended December 31, 2018, 2017 and 2016. MPLX’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.
(In millions) | 2018 |  | 2017 |  | 2016
General partner's distributions: |  |  |  |  |
General partner's distributions on general partner units | $ | — |  |  | $ | 25 |  |  | $ | 18 |
General partner's distributions on IDRs(1) | — |  |  | 303 |  |  | 187 |
Total distribution on general partner units and IDRs | — |  |  | 328 |  |  | 205 |
Limited partners' distributions: |  |  |  |  |
Common unitholders, includes common units of general partner | 1,985 |  |  | 895 |  |  | 692 |
Preferred unit distributions | 75 |  |  | 65 |  |  | 41 |
Total cash distributions declared | $ | 2,060 |  |  | $ | 1,288 |  |  | $ | 938 |
(1) | Includes distributions of fourth quarter 2017 income declared on general partner common units issued February 1, 2018 in exchange for the economic general partner interest.

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