Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019
Revenues and other income:
Total revenues from contracts with customers	$ 1,592		$ 1,717	[1]	$ 3,373		$ 3,425	[1]
Rental income	98		93	[2]	194		192	[2]
Rental income - related parties	237		286	[2]	471		611	[2]
Income/(loss) from equity method investments(2)	89		83	[2],[3]	(1,095)	[4],[5]	160	[2],[6]
Other income	2		4	[2]	3		4	[2]
Other income - related parties	63		27	[2]	127		53	[2]
Revenues	2,081		2,210	[1],[2]	3,073		4,445	[1],[2]
Costs and expenses:
Rental cost of sales	33		29	[2]	68		66	[2]
Rental cost of sales - related parties	41		36	[2]	87		79	[2]
Purchases - related parties	280		313	[2]	556		591	[2]
Depreciation and amortization	321	[7]	313	[2],[3],[7]	646		614	[2],[6]
Goodwill and Intangible Asset Impairment	0		0	[2],[3]	2,165		0	[2],[6]
General and administrative expenses	96		90	[2]	193		191	[2]
Other taxes	30		25	[2]	61		55	[2]
Costs and Expenses	1,203		1,325	[2]	4,681		2,648	[2]
Income/(loss) from operations	878		885	[2]	(1,608)		1,797	[2]
Related party interest and other financial costs	1		2	[2]	4		3	[2]
Interest expense (net of amounts capitalized of $10 million, $12 million, $23 million and $23 million, respectively)	206		214	[2]	417		428	[2]
Other financial costs	16		13	[2]	32		22	[2]
Income/(loss) before income taxes	655		656	[2]	(2,061)		1,344	[2]
(Benefit)/provision for income taxes	0		(1)	[2],[3]	0		(2)	[2]
Net income	655		657	[2],[3],[8]	(2,061)		1,346	[2],[6],[8]
Less: Net income (loss) attributable to noncontrolling interest	7		6	[2]	15		12	[2]
Income (Loss) Attributable to Predecessor	0		169	[2]	0		349	[2]
Net income (loss) attributable to MPLX LP	648	[9]	482	[2],[10]	(2,076)	[11]	985	[2],[12]
Limited partners' interest in net income (loss) attributable to MPLX LP	617		461	[2]	(2,138)		944	[2]
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	$ 617	[9]	$ 440	[10]	$ (2,138)	[11]	$ 923	[12]
Net income (loss) attributable to MPLX LP per limited partner unit:
Common - basic (in USD per unit)	$ 0.58		$ 0.56	[2]	$ (2.02)		$ 1.16	[2]
Common - diluted (in USD per unit)	$ 0.58		$ 0.55	[2]	$ (2.02)		$ 1.16	[2]
Weighted average limited partner units outstanding:
Common - basic (in shares)	1,059		794	[2],[13]	1,059		794	[2],[14]
Common - diluted (in shares)	1,059		795	[2],[13]	1,059		795	[2],[14]
Service [Member]
Revenues and other income:
Total revenues from contracts with customers	$ 563		$ 619	[1],[2]	$ 1,175		$ 1,233	[1],[2]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	857		847	[1],[2]	1,785		1,650	[1],[2]
Service, Other [Member]
Revenues and other income:
Total revenues from contracts with customers	22		26	[1],[2]	61		60	[1],[2]
Product [Member]
Revenues and other income:
Total revenues from contracts with customers	120		189	[2]	289		405	[2]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	30		36	[1],[2]	63		77	[1],[2]
Oil and Gas, Refining and Marketing [Member]
Costs and expenses:
Cost of Goods and Services Sold	315		353	[2]	683		692	[2]
Natural Gas, Midstream [Member]
Costs and expenses:
Cost of Goods and Services Sold	87		166	[2]	222		360	[2]
Series A Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net income (loss) attributable to MPLX LP	21	[9]	21	[10]	41	[11]	41	[12]
Dividends, Preferred Stock	21		21	[2]	41		41	[2]
Series B Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net income (loss) attributable to MPLX LP	10	[9]	21	[10]	21	[11]	21	[12]
Dividends, Preferred Stock	$ 10		$ 0	[2]	$ 21		$ 0	[2]

[1] Financial information for the three and six months ended June 30, 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[2] Financial information for the three and six months ended June 30, 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[3] Financial information for the three and six months ended June 30, 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

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

[5] The six months ended June 30, 2020 includes $1,264 million of impairment expense. See Note 4.

[6] Financial information for the six months ended June 30, 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[7] Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $146 million and $304 million for the three and six months ended June 30, 2020, respectively, and $163 million and $316 million for the three and six months ended June 30, 2019, respectively. Third party revenues for the G&P segment were $748 million and $323 million for the three and six months ended June 30, 2020, respectively, and $851 million and $1,738 million for the three and six months ended June 30, 2019, respectively.

[8] Financial information for the three and six months ended June 30, 2019 has been retrospectively adjusted for the acquisition of ANDX. See Notes 1 and 3.

[9] 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.

[10] 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.

[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.

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

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