Net Income Per Limited Partner Unit - Schedule of Distributions by Partner by Class (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2022		Sep. 30, 2021		Sep. 30, 2022		Sep. 30, 2021
Net Income Per Share [Line Items]
Net Income (Loss) Attributable to Parent	[1]	$ 1,428	[2]	$ 802		$ 3,128	[2]	$ 2,247
Distribution Made to Limited Partner, Cash Distributions Declared		810		1,353	[3]	2,300		2,827	[3]
Undistributed net income (loss) attributable to MPLX LP		618	[2]	(551)		828	[2]	(580)
Limited Partners Common Units [Member]
Net Income Per Share [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared		777		1,305	[3],[4]	2,204		2,717	[3]
Undistributed net income (loss) attributable to MPLX LP		600	[2]	(551)		804	[2]	(580)
Series A Preferred Stock [Member] | Series A Preferred Stock [Member]
Net Income Per Share [Line Items]
Net Income (Loss) Attributable to Parent	[1]	41	[2]	38		89	[2]	79
Distribution Made to Limited Partner, Cash Distributions Declared		23		38	[3],[4]	65		79	[3],[4]
Undistributed net income (loss) attributable to MPLX LP		18	[2]	0		24	[2]	0
Series B Preferred Stock [Member] | Series A Preferred Stock [Member]
Net Income Per Share [Line Items]
Net Income (Loss) Attributable to Parent	[1]	10	[2]	10		31	[2]	31
Distribution Made to Limited Partner, Cash Distributions Declared		10		10		31		31
Undistributed net income (loss) attributable to MPLX LP		0	[2]	0		0	[2]	0
Common Stock | Limited Partners Common Units [Member]
Net Income Per Share [Line Items]
Net Income (Loss) Attributable to Parent	[1]	$ 1,377	[2]	$ 754		$ 3,008	[2]	$ 2,137

[1] 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.

[2] The three and nine months ended September 30, 2022 include a $509 million non-cash gain on a lease reclassification. See Note 14 for additional information.

[3] 2021 periods include the Supplemental Distribution Amount.

[4] Includes a supplemental distribution amount of $0.575 per common unit declared and paid during the fourth quarter of 2021 (the “Supplemental Distribution Amount”)