Equity (Changes in Partners Capital, Unit Rollforward) (Details) - shares					12 Months Ended
		Feb. 01, 2018	Sep. 01, 2017	Mar. 01, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders Equity [Line Items]
Beginning balance, number of units					794,089,518	415,438,793	368,555,271
Unit-based compensation awards, in units					288,031	348,527	273,639
Units issued							14,129,589
Unit conversion					1,148,330	264,413,309	366,509
Ending balance, number of units					1,058,355,471	794,089,518	415,438,793
Aggregate percentage of general partner interest		2.00%		2.00%	2.00%
LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Aggregate percentage of general partner interest			2.00%
Refining Logistics & Fuels Distribution [Member]
Stockholders Equity [Line Items]
Units, acquisitions						113,888,889
HST & WHC & MPLXT
Stockholders Equity [Line Items]
Units, acquisitions							13,224,873
LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions							18,888,912
Andeavor Logistics [Member]
Stockholders Equity [Line Items]
Units, acquisitions					262,829,592
Limited Partners Common Units
Stockholders Equity [Line Items]
Beginning balance, number of units					794,089,518	407,130,020	357,193,288
Unit-based compensation awards, in units					288,031	348,387	268,167
Units issued					0		13,846,998
Unit conversion		275,000,000			1,148,330	275,000,000	4,350,057
Ending balance, number of units					1,058,355,471	794,089,518	407,130,020
Limited Partners Common Units | Refining Logistics & Fuels Distribution [Member]
Stockholders Equity [Line Items]
Units, acquisitions						111,611,111
Limited Partners Common Units | HST & WHC & MPLXT
Stockholders Equity [Line Items]
Units, acquisitions							12,960,376
Limited Partners Common Units | LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions							18,511,134
Limited Partners Common Units | Andeavor Logistics [Member]
Stockholders Equity [Line Items]
Units, acquisitions					262,829,592
Class B Units
Stockholders Equity [Line Items]
Beginning balance, number of units					0	0	3,990,878
Unit conversion							3,990,878
Ending balance, number of units					0	0	0
General Partner Units
Stockholders Equity [Line Items]
Beginning balance, number of units	[1]				0	8,308,773	7,371,105
Unit-based compensation awards, in units	[1]				0	140	5,472
Units issued	[1]						282,591
Unit conversion	[1]				0	10,586,691	7,330
Ending balance, number of units	[1]				0	0	8,308,773
General Partner Units | LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions			377,778
General Partner Units | Refining Logistics & Fuels Distribution [Member]
Stockholders Equity [Line Items]
Units, acquisitions	[1]					2,277,778
General Partner Units | HST & WHC & MPLXT
Stockholders Equity [Line Items]
Units, acquisitions				264,497			264,497	[1]
General Partner Units | LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions	[1]						377,778
General Partner Units | Andeavor Logistics [Member]
Stockholders Equity [Line Items]
Units, acquisitions	[1]				0

[1] Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest.