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v3.8.0.1

Debt Debt - Summary of Outstanding Borrowings - Interest Rates and Table Due Dates (Details) | 3 Months Ended |
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Mar. 31, 2018 | Feb. 10, 2017
MarkWest [Member] | Senior Notes [Member] | 5.500% senior notes due February 2023 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 5.50% |
Debt Instrument, Maturity Date | Feb. 15, 2023 |
MarkWest [Member] | Senior Notes [Member] | 4.500% senior notes due July 2023 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.50% |
Debt Instrument, Maturity Date | Jul. 15, 2023 |
MarkWest [Member] | Senior Notes [Member] | 4.875% senior notes due December 2024 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.875% |
Debt Instrument, Maturity Date | Dec. 01, 2024 |
MarkWest [Member] | Senior Notes [Member] | 4.875% senior notes due June 2025 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.875% |
Debt Instrument, Maturity Date | Jun. 01, 2025 |
MPLX LP | Line of Credit [Member] | Bank revolving credit facility due 2022 |  |
Debt Instrument [Line Items] |  |
Expiration date | Jul. 21, 2022 |
MPLX LP | Senior Notes [Member] | 5.500% senior notes due February 2023 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 5.50% |
Debt Instrument, Maturity Date | Feb. 15, 2023 |
MPLX LP | Senior Notes [Member] | Senior Notes Due March 2023 [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.375% |
Debt Instrument, Maturity Date | Mar. 15, 2023 |
MPLX LP | Senior Notes [Member] | 4.500% senior notes due July 2023 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.50% |
Debt Instrument, Maturity Date | Jul. 15, 2023 |
MPLX LP | Senior Notes [Member] | 4.875% senior notes due December 2024 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.875% |
Debt Instrument, Maturity Date | Dec. 01, 2024 |
MPLX LP | Senior Notes [Member] | 4.000% senior notes due February 2025 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.00% |
Debt Instrument, Maturity Date | Feb. 15, 2025 |
MPLX LP | Senior Notes [Member] | 4.875% senior notes due June 2025 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.875% |
Debt Instrument, Maturity Date | Jun. 01, 2025 |
MPLX LP | Senior Notes [Member] | 4.125% senior notes due March 2027 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.125% | 4.125%
Debt Instrument, Maturity Date | Mar. 01, 2027 |
MPLX LP | Senior Notes [Member] | Senior Notes Due March 2028 [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.00% |
Debt Instrument, Maturity Date | Mar. 15, 2028 |
MPLX LP | Senior Notes [Member] | Senior Notes Due April 2038 [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.50% |
Debt Instrument, Maturity Date | Apr. 15, 2038 |
MPLX LP | Senior Notes [Member] | 5.200% senior notes due March 2047 |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 5.20% | 5.20%
Debt Instrument, Maturity Date | Mar. 01, 2047 |
MPLX LP | Senior Notes [Member] | Senior Notes Due April 2048 [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.70% |
Debt Instrument, Maturity Date | Apr. 15, 2048 |
MPLX LP | Senior Notes [Member] | Senior Notes Due April 2058 [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 4.90% |
Debt Instrument, Maturity Date | Apr. 15, 2058 |
Marathon Pipe Line LLC [Member] | Capital Lease Obligations [Member] |  |
Debt Instrument [Line Items] |  |
Capital Lease Due Date Year | 2020 |

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