Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2020		Mar. 31, 2019
Equity Method Investment, Other than Temporary Impairment		$ 1,264
Revenues and other income:
Total revenues from contracts with customers		1,781		$ 1,708	[1]
Rental income		96		99	[2]
Rental income - related parties		234		325	[2]
Income/(loss) from equity method investments(2)		(1,184)	[3],[4],[5]	77	[2],[6],[7],[8]
Other income		1		0	[2]
Other income - related parties		64		26	[2]
Revenues		992		2,235	[1],[2]
Costs and expenses:
Rental cost of sales		35		37	[2]
Rental cost of sales - related parties		46		43	[2]
Purchases - related parties		276		278	[2]
Depreciation and amortization	[9]	325		301	[2],[6],[7]
General and administrative expenses		97		101	[2]
Other taxes		31		30	[2]
Total costs and expenses		3,478		1,323	[2]
Income/(loss) from operations		(2,486)		912	[2]
Related party interest and other financial costs		3		1	[2]
Interest expense (net of amounts capitalized of $13 million and $11 million, respectively)		211		214	[2]
Other financial costs		16		9	[2]
Income/(loss) before income taxes		(2,716)		688	[2]
(Benefit)/provision for income taxes		0		(1)	[2],[7]
Net income		(2,716)		689	[2],[6],[7],[10]
Less: Net income (loss) attributable to noncontrolling interest		8		6	[2]
Income (Loss) Attributable to Predecessor		0		180	[2]
Net income (loss) attributable to MPLX LP		(2,724)	[11]	503	[2],[12]
Limited partners' interest in net income (loss) attributable to MPLX LP		(2,755)		483	[2]
Weighted average limited partner units outstanding:
Goodwill and Intangible Asset Impairment		2,165		0	[2],[6],[7]
Limited Partners Common Units
Costs and expenses:
Net income (loss) attributable to MPLX LP		$ (2,755)	[11]	$ 483	[12]
Net income (loss) attributable to MPLX LP per limited partner unit:
Common - basic (in USD per unit)		$ (2.60)		$ 0.61	[2]
Common - diluted (in USD per unit)		$ (2.60)		$ 0.61	[2]
Weighted average limited partner units outstanding:
Common - basic (in shares)		1,058		794	[2]
Common - diluted (in shares)		1,058		795	[2]
Service [Member]
Revenues and other income:
Total revenues from contracts with customers		$ 612		$ 614	[1],[2]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		928		803	[1],[2]
Service, Other [Member]
Revenues and other income:
Total revenues from contracts with customers		39		34	[1],[2]
Product [Member]
Revenues and other income:
Total revenues from contracts with customers		169		216	[2]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		33		41	[1],[2]
Oil and Gas, Refining and Marketing [Member]
Costs and expenses:
Cost of Goods and Services Sold		368		339	[2]
Natural Gas, Midstream [Member]
Costs and expenses:
Cost of Goods and Services Sold		135		194	[2]
Series A Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net income (loss) attributable to MPLX LP		20	[11]	20	[12]
Dividends, Preferred Stock		20		20	[2]
Series B Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net income (loss) attributable to MPLX LP	[11]	11
Dividends, Preferred Stock		$ 11		$ 0	[2]

[1] Financial information for the first quarter of 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[2] Financial information for the first quarter of 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[3] The 2020 period includes $1,264 million of impairment expense. See Note 4.

[4] The 2020 period includes $1,264 million of impairment expense. See Note 4.

[5] Includes the impact of any basis differential amortization or accretion in addition to the impairment of $1,264 million.

[6] Financial information for the first quarter of 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[7] Financial information for the first quarter of 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[8] Financial information for the first quarter of 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[9] Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $158 million and $153 million for the three months ended March 31, 2020 and 2019, respectively. Third party losses for the G&P segment were $425 million for the three months ended March 31, 2020 and third party revenues were $887 million for the three months ended March 31, 2019.

[10] Financial information for the first quarter of 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[11] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[12] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.