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Acquisitions MarEn Bakken (Details) $ in Millions			3 Months Ended
		Feb. 15, 2017 USD ($) Quarterly_reporting_period	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates			$ 38.0	$ 554.0
Income from equity method investments	[1]		61.0	$ 5.0
Equity method investments			4,033.0		$ 4,010.0
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%
Income from equity method investments			$ 7.0
Bakken Pipeline System [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of Ownership Interest in Joint Venture Acquired		37.00%
Equity method investment, ownership percentage		9.00%
MarEn Bakken Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage			25.00%
Equity method investments			$ 529.0		$ 520.0
MarEn Bakken Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates		$ 2,000.0
MPC
Schedule of Equity Method Investments [Line Items]
Incentive Distribution Rights Forfeited per Quarter		$ 1.6
Number of Quarters IDRs Forfeited | Quarterly_reporting_period		12
Prorated Incentive Distribution Rights Forfeited		$ 0.8
[1] “Income (loss) from equity method investments” includes the impact of any basis differential amortization or accretion.

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