Segment Information - Reconciliation Adjusted EBITDA to Net income (Details) - USD ($) $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	[5]	Mar. 31, 2019	[5]	Dec. 31, 2018	[5]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Depreciation and amortization	[1]												$ 1,254	$ 867	$ 683
Provision for income taxes													0	8	1
Amortization of deferred financing costs													42	55	53
Extinguishment of Debt, Gain (Loss), Net of Tax													0	(46)	0
Total compensation expense													(22)	(23)	(15)
Goodwill and Intangible Asset Impairment													(1,197)	0	0
Interest and Other Financial Costs													873	613	301
Income (Loss) from Equity Method Investments	[2],[3]												290	247	78
Distributions from unconsolidated affiliates													525	412	241
Unrealized gains	[4]														(6)
Acquisition Costs, Period Cost													(14)	(4)	(11)
Other Cost and Expense, Operating													(1)	0	0
Net income		$ (573)	$ 689	$ 657		$ 689		$ 611		$ 516	$ 456	$ 423	1,462	2,006	836
Logistics and Storage [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization													(503)	(308)	(163)
Gathering and Processing [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization													(751)	(559)	(520)
Operating Segments
Segment Reporting Information [Line Items]
Adjusted EBITDA													4,334	3,475	2,004
Amortization of deferred financing costs													42	55	53
Operating Segments | Logistics and Storage [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	[6]												2,748	2,057	775
Income (Loss) from Equity Method Investments													200	171	36
Operating Segments | Gathering and Processing [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	[6]												1,586	1,418	1,229
Income (Loss) from Equity Method Investments													90	76	42
Segment Reconciling Items
Segment Reporting Information [Line Items]
Distributions from unconsolidated affiliates													562	458	231
Adjusted EBITDA attributable to noncontrolling interests													32	18	8
Adjusted EBITDA attributable to Predecessor	[7]												770	335	$ 47
Not Designated as Hedging Instrument
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	[4]												$ 1	$ 5

[1] Depreciation and amortization attributable to L&S was $503 million, $308 million and $163 million for the years ended 2019, 2018 and 2017, respectively. Depreciation and amortization attributable to G&P was $751 million, $559 million and $520 million for 2019, 2018 and 2017, respectively.

[2] “Income from equity method investments” includes the impact of any basis differential amortization or accretion.

[3] The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1 for additional information

[4] MPLX makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

[5] As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million, $1,646 million and $1,629 million, respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million, $678 million and $659 million, respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million, $509 million and $488 million, respectively.

[6] See below for the reconciliation from Segment Adjusted EBITDA to “Net income.”

[7] The Adjusted EBITDA adjustments related to Predecessor are excluded from Adjusted EBITDA attributable to MPLX LP prior to the acquisition date.