Segment Information - Segment Adjusted EBITDA (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019
Segment Reporting Information [Line Items]
Restructuring Charges		$ 36	$ 0		$ 36		$ 0
Depreciation and amortization	[1]	346	302		992		916
Total revenues from contracts with customers		1,756	1,760		5,129		5,185
Rental income		102	99		296		291
Income/(loss) from equity method investments(1)		83	95		(1,012)	[2],[3]	255
Other income		2	2		5		6
Total segment revenues and other income		(2,247)	(2,280)		(5,320)		(6,725)
Investments in unconsolidated affiliates					(244)		(494)
L&S
Segment Reporting Information [Line Items]
Depreciation and amortization		164	113		440		373
Total revenues from contracts with customers		998	998		2,973		2,844
Investments in unconsolidated affiliates		(4)	(95)		(132)		(163)
G&P
Segment Reporting Information [Line Items]
Depreciation and amortization		182	189		552		543
Total revenues from contracts with customers		758	762		2,156		2,341
Investments in unconsolidated affiliates		(18)	(76)		(112)		(331)
Operating Segments
Segment Reporting Information [Line Items]
Adjusted EBITDA		1,335	1,165		3,856		3,015
Operating Segments | L&S
Segment Reporting Information [Line Items]
Restructuring Charges		27	0		27		0
Rental income		249	304		737		935
Income/(loss) from equity method investments(1)		36	60		126		159
Other income		51	17		154		45
Total segment revenues and other income	[4]	(1,334)	(1,379)		(3,990)		(3,983)
Adjusted EBITDA	[5]	893	766		2,604		1,895
Capital Expenditure		118	272		410		700
Operating Segments | G&P
Segment Reporting Information [Line Items]
Restructuring Charges		9	0		9		0
Rental income		94	88		271		260
Income/(loss) from equity method investments(1)		47	35		(1,138)		96
Other income		14	16		41		45
Total segment revenues and other income	[4]	(913)	(901)		(1,330)		(2,742)
Adjusted EBITDA	[5]	442	399		1,252		1,120
Capital Expenditure		131	321		375		953
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA attributable to Predecessor		0	108	[6]	0		770	[6]
Service [Member]
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		604	632		1,779		1,865
Service [Member] | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		87	95		248		260
Service [Member] | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		517	537		1,531		1,605
Service [Member] | Operating Segments | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		989	976		2,924		2,787
Service [Member] | Operating Segments | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		524	555		1,549		1,627
Product [Member]
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		165	171		454		576
Product [Member] | Operating Segments | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		9	22		49		57
Product [Member] | Operating Segments | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		234	207		607		714
Third Party [Member] | L&S
Segment Reporting Information [Line Items]
Total segment revenues and other income		(139)	(182)		(443)		(498)
Third Party [Member] | G&P
Segment Reporting Information [Line Items]
Total segment revenues and other income		$ (858)	$ (843)		$ (1,181)		$ (2,581)

[1] 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.

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

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

[4] Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $139 million and $443 million for the three and nine months ended September 30, 2020, respectively, and $182 million and $498 million for the three and nine months ended September 30, 2019, respectively. Third party revenues for the G&P segment were $858 million and $1,181 million for the three and nine months ended September 30, 2020, respectively, and $843 million and $2,581 million for the three and nine months ended September 30, 2019, respectively.

[5] See below for the reconciliation from Segment Adjusted EBITDA to net income.

[6] The adjusted EBITDA adjustments related to Predecessor are excluded from adjusted EBITDA attributable to MPLX LP prior to the Merger.