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MPLX LP - Dropdowns to MPLX and GP/IDR Exchange(Details) - MPLX LP - USD ($) shares in Thousands, $ in Millions | Feb. 01, 2018 | Jan. 02, 2018 | Sep. 01, 2017 | Mar. 01, 2017
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MPLX 364-day term loan |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |
Maximum borrowing capacity | $ 4,100 | $ 4,100 |  |
Debt instrument, term | 364 days | 364 days |  |
Cash and Cash Equivalents |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |
Payments to acquire business, gross | $ 4,100 |  | $ 420 | $ 1,500
Limited Partner |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |
Units issued, number of units | 112,000 |  | 19,000 | 13,000
Conversion of stock, shares issued | 275,000 |  |  |
General Partner |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |
Units issued, number of units | 2,000 |  | 378 | 264

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