Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019
Restructuring Charges		$ 36		$ 0		$ 36		$ 0
Revenues and other income:
Total revenues from contracts with customers		1,756		1,760		5,129		5,185
Rental income		102		99		296		291
Rental income - related parties		241		293		712		904
Income/(loss) from equity method investments(1)		83		95		(1,012)	[1],[2]	255
Other income		2		2		5		6
Other income - related parties		63		31		190		84
Revenues		2,247		2,280		5,320		6,725
Costs and expenses:
Rental cost of sales		33		37		101		103
Rental cost of sales - related parties		32		45		119		124
Purchases - related parties		297		303		853		894
Depreciation and amortization	[3]	346		302		992		916
Goodwill and Intangible Asset Impairment		0		0		2,165		0
General and administrative expenses		96		102		289		293
Other taxes		33		29		94		84
Costs and Expenses		1,348		1,354		6,029		4,002
Income/(loss) from operations		899		926		(709)		2,723
Related party interest and other financial costs		0		5		4		8
Interest expense (net of amounts capitalized of $8 million, $13 million, $31 million and $36 million, respectively)		207		212		624		640
Other financial costs		17		16		49		38
Income/(loss) before income taxes		675		693		(1,386)		2,037
Provision for income taxes		1		4		1		2
Net income		674		689		(1,387)		2,035
Less: Net income (loss) attributable to noncontrolling interest		9		8		24		20
Income (Loss) Attributable to Predecessor		0		52		0		401
Net income (loss) attributable to MPLX LP		665	[4]	629	[5]	(1,411)	[6]	1,614	[7]
Limited partners' interest in net income (loss) attributable to MPLX LP		635		602		(1,503)		1,546
Weighted average limited partner units outstanding:
Equity Method Investment, Other than Temporary Impairment						1,264
Limited Partners Common Units
Costs and expenses:
Net income (loss) attributable to MPLX LP		$ 635	[4]	$ 599	[5]	$ (1,503)	[6]	$ 1,522	[7]
Net income (loss) attributable to MPLX LP per limited partner unit:
Common - basic (in USD per unit)		$ 0.61		$ 0.61		$ (1.43)		$ 1.78
Common - diluted (in USD per unit)		$ 0.61		$ 0.61		$ (1.43)		$ 1.78
Weighted average limited partner units outstanding:
Common - basic (in shares)		1,046		974	[8]	1,054		855	[9]
Common - diluted (in shares)		1,047		975	[8]	1,054		855	[9]
Service [Member]
Revenues and other income:
Total revenues from contracts with customers		$ 604		$ 632		$ 1,779		$ 1,865
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		909		899		2,694		2,549
Service, Other [Member]
Revenues and other income:
Total revenues from contracts with customers		41		26		102		86
Product [Member]
Revenues and other income:
Total revenues from contracts with customers		165		171		454		576
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		37		32		100		109
Oil and Gas, Refining and Marketing [Member]
Costs and expenses:
Cost of Goods and Services Sold		323		407		1,006		1,099
Natural Gas, Midstream [Member]
Costs and expenses:
Cost of Goods and Services Sold		152		129		374		489
Series A Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net income (loss) attributable to MPLX LP		20	[4]	20	[5]	61	[6]	61	[7]
Dividends, Preferred Stock		20		20		61		61
Series B Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net income (loss) attributable to MPLX LP		10	[4]	10	[5]	31	[6]	31	[7]
Dividends, Preferred Stock		10		7		31		7
MPC
Revenues and other income:
Rental income - related parties		241		293		712		904
Other income - related parties		48		14		144		34
MPC | Service [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		908		899		2,692		2,549
MPC | Product [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[10]	$ 37		$ 32		$ 100		$ 109

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

[2] The nine months ended September 30, 2020 includes $1,264 million of impairment expense. See Note 4.

[3] Depreciation and amortization attributable to L&S was $164 million and $440 million for the three and nine months ended September 30, 2020, respectively, and $113 million and $373 million for the three and nine months ended September 30, 2019, respectively. Depreciation and amortization attributable to G&P was $182 million and $552 million for the three and nine months ended September 30, 2020, respectively, and $189 million and $543 million for the three and nine months ended September 30, 2019, respectively.

[4] 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.

[5] 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.

[6] 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.

[7] 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.

[8] The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire three months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

[9] The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire nine months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

[10] There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For the three and nine months ended September 30, 2020, these sales totaled $107 million and $332 million, respectively. For the three and nine months ended September 30, 2019, these sales totaled $301 million and $819 million, respectively.