Segment Information - Revenues and Adjusted EBITDA (Details) - USD ($) $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	[1]	Mar. 31, 2019	[1]	Dec. 31, 2018	[1]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income		$ 2,316	$ 2,280	$ 2,210		$ 2,235		$ 2,295		$ 1,712	$ 1,578	$ 1,420	$ 9,041	$ 7,005	$ 3,867
Revenue from Contract with Customer, Excluding Assessed Tax													7,041	5,449
Rental income													388	352	277
Income (Loss) from Equity Method Investments	[2],[3]												290	247	78
Other income													12	7	6
Investments in unconsolidated affiliates													(713)	(341)	(761)
Revenues	[4]														(6)
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted EBITDA													4,334	3,475	2,004
Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,856	2,598
Investments in unconsolidated affiliates													289	3	533
Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income	[5]												5,352	3,672	1,562
Rental income													1,235	856	279
Income (Loss) from Equity Method Investments													200	171	36
Other income													61	47	47
Adjusted EBITDA	[6]												2,748	2,057	775
Capital Expenditure													1,060	708	512
Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,185	2,851
Investments in unconsolidated affiliates													424	338	228
Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income	[5]												3,689	3,333	2,305
Rental income													349	342	277
Income (Loss) from Equity Method Investments													90	76	42
Other income													65	59	51
Adjusted EBITDA	[6]												1,586	1,418	1,229
Capital Expenditure													1,203	1,545	972
Service [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,498	1,856	1,156
Service [Member] | Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													346	174
Service [Member] | Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,765	2,575	1,200
Service [Member] | Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,152	1,682
Service [Member] | Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,188	1,685	1,038
Product [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													806	887	889
Product [Member] | Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													91	23	0
Product [Member] | Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													997	1,171	897
Third Party | Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income													660	371	160
Third Party | Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income													$ 3,474	$ 3,198	$ 2,246

[1] 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.

[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] Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $660 million, $371 million and $160 million for 2019, 2018 and 2017, respectively. Third party revenues for the G&P segment were $3,474 million, $3,198 million and $2,246 million for 2019, 2018 and 2017, respectively.

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