Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 1,462	$ 2,006	$ 836
Other comprehensive income/(loss), net of tax:
Remeasurements of pension and other postretirement benefits related to equity method investments, net of tax	1	(2)	0
Comprehensive income	1,463	2,004	836
Less comprehensive income attributable to:
Noncontrolling interests	28	16	6
Income attributable to Predecessor	401	172	36
Comprehensive income attributable to MPLX LP	$ 1,034	$ 1,816	$ 794