Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	[1]	Jun. 30, 2020	Jun. 30, 2019	[1]
Statement of Comprehensive Income [Abstract]
Net (loss)/income	$ 655	$ 657	[2],[3]	$ (2,061)	$ 1,346	[2],[4]
Other comprehensive income/(loss), net of tax:
Remeasurements of pension and other postretirement benefits related to equity method investments, net of tax	0	0		(1)	1
Comprehensive income/(loss)	655	657		(2,062)	1,347
Less comprehensive income attributable to:
Noncontrolling interests	7	6		15	12
Comprehensive Income (loss), Net of Tax, Attributable to Predecessor	0	169		0	349
Comprehensive income/(loss) attributable to MPLX LP	$ 648	$ 482		$ (2,077)	$ 986

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