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Equity (Changes in Partners Capital, Unit Rollforward) (Details) - shares							12 Months Ended
		Feb. 01, 2018	Sep. 01, 2017	Mar. 01, 2017	Sep. 01, 2016	Mar. 31, 2016	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Stockholders Equity [Line Items]
Beginning balance, number of units							415,438,793		368,555,271		311,469,407
Unit-based compensation awards, in units							348,527		273,639		123,459
Units issued									14,129,589		26,885,597
Unit conversion									366,509		366,509
Units, acquisitions											22,993,880
Units contributed											6,716,419
Ending balance, number of units							794,089,518		415,438,793		368,555,271
Aggregate percentage of general partner interest		2.00%		2.00%		2.00%	2.00%
LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions							264,413,309
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
Limited Partners Common Units
Stockholders Equity [Line Items]
Beginning balance, number of units							407,130,020		357,193,288		296,687,176
Unit-based compensation awards, in units							348,387		268,167		120,989
Units issued							0		13,846,998		26,347,887
Unit conversion		275,000,000					275,000,000		4,350,057		4,350,057
Units, acquisitions											22,534,002
Units contributed					21,401,137						7,153,177
Ending balance, number of units							794,089,518		407,130,020		357,193,288
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
Class B Units
Stockholders Equity [Line Items]
Beginning balance, number of units							0		3,990,878		7,981,756
Unit conversion									(3,990,878)		(3,990,878)
Ending balance, number of units							0		0		3,990,878
General Partner Units
Stockholders Equity [Line Items]
Beginning balance, number of units							8,308,773	[1]	7,371,105		6,800,475	[1]
Unit-based compensation awards, in units	[1]						140		5,472		2,470
Units issued	[1]								282,591		537,710
Unit conversion	[1]						(10,586,691)		7,330		7,330
Units, acquisitions	[1]										459,878
Units contributed					436,758						(436,758)	[1]
Ending balance, number of units							0	[1]	8,308,773	[1]	7,371,105
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
[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.

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Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

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The number of each class of partnership units outstanding at the balance sheet date. Units represent shares of ownership of the general, limited, and preferred partners.

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Change in the number of units for each class of partners' capital accounts during the year due to acquisitions. Partners include general, limited and preferred partners.

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Units contributed by each class of partners during the year. Units represent shares of ownership of the general, limited, and preferred partners.

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The number of units converted into shares of each class of partners' capital account. Units represent shares of ownership of the general, limited, and preferred partners.

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Total units issued during the year due to the sale of units. All partners include general, limited and preferred partners.

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