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Investments & NCI MarEn Bakken (Details) $ in Millions		6 Months Ended
	Feb. 15, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates		$ 640.0	$ 39.0
Equity method investments		$ 3,368.0		$ 2,471.0
Bakken Pipeline System [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of Ownership Interest in Joint Venture Acquired	36.75%
Equity Method Investment, Ownership Percentage		9.1875%
MarEn Bakken [Member]
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates	$ 500.0
Percentage of Ownership Interest in Joint Venture Acquired		25.00%
Equity method investments		$ 519.0
MPC
Schedule of Equity Method Investments [Line Items]
Incentive Distribution Rights Forfeited per Quarter	$ 1.6
Number of Quarters IDRs Forfeited	12
Prorated Incentive Distribution Rights Forfeited	$ 0.8
MarEn Bakken Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates	$ 2,000.0

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Section 50
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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