Investments and Noncontrolling Interest (Equity Method Investments) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018	Sep. 01, 2017
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 5,275	$ 4,901
Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		38.00%
Wink to Webster Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		15.00%
Centrahoma Processing LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		40.00%
Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%		25.00%
Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		35.00%		35.00%
LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		41.00%		41.00%
MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%
MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		67.00%
Rendezvous Gas Services, L.L.C. [Member] | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	78.00%
MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		56.00%
Sherwood Midstream LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		50.00%
Sherwood Midstream Holdings | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		53.00%
Andeavor Logistics Rio Pipeline [Member] | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	67.00%
Minnesota Pipe Line Company, LLC [Member] | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	17.00%
Logistics and Storage [Member] | Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 134	0
Logistics and Storage [Member] | Wink to Webster Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		126	0
Logistics and Storage [Member] | Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investments		83	90
Logistics and Storage [Member] | Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investments		265	275
Logistics and Storage [Member] | LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investments		238	226
Logistics and Storage [Member] | MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Equity method investments		481	498
Logistics and Storage [Member] | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	55	51
Logistics and Storage [Member] | Andeavor Logistics Rio Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	202	181
Logistics and Storage [Member] | Minnesota Pipe Line Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	190	197
Gathering and Processing [Member] | Centrahoma Processing LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments		153	160
Gathering and Processing [Member] | MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		302	236
Gathering and Processing [Member] | Rendezvous Gas Services, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	170	248
Gathering and Processing [Member] | MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investments		1,984	2,039
Gathering and Processing [Member] | Sherwood Midstream LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments		537	366
Gathering and Processing [Member] | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity method investments		157	157
Gathering and Processing [Member] | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	198	177
Operating Segments | Logistics and Storage [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		1,774	1,518
Operating Segments | Gathering and Processing [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 3,501	$ 3,383

[1] These investments as well as certain investments included within “Other” for both L&S and G&P are investments acquired as part of the Merger. The December 31, 2019 balance reflects all purchase accounting adjustments identified by MPC as part of its acquisition of Andeavor.