Acquisitions & Divestitures Pro Forma (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	$ 45.4	$ (197.0)	$ 122.3	$ (1,060.8)
Earnings Per Share, Basic	$ 0.19	$ (0.90)	$ 0.51	$ (5.21)
Earnings Per Share, Diluted	$ 0.19	$ (0.90)	$ 0.51	$ (5.21)
Revenues	$ 383.7	$ 333.7	$ 803.8	$ 595.0
2016 Permian Basin Acquisition [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)		$ (197.0)		$ (1,060.8)
Earnings Per Share, Basic		$ (0.90)		$ (5.21)
Earnings Per Share, Diluted		$ (0.90)		$ (5.21)
Pro Forma Revenue		$ 338.7		$ 604.6
Pro Forma Net Income (Loss)		$ (197.5)		$ (1,062.0)
Pro Forma Earnings Per Share, Basic		$ (0.91)		$ (5.21)
Pro Forma Earnings Per Share, Diluted		$ (0.91)		$ (5.21)
Revenues		$ 333.7		$ 595.0

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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