Acquisitions & Divestitures Pinedale Divestiture (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017
Divestitures [Line Items]
Proceeds from disposition of assets			$ 666.7	$ 48.8
Net gain (loss) from asset sales, inclusive of restructuring costs	$ 17.8	$ (3.9)	4.6	(0.4)
Income (loss) before income taxes	78.5	$ (442.2)	(150.2)	$ (509.7)
Pinedale Divestiture [Member]
Divestitures [Line Items]
Proceeds from disposition of assets					$ 718.2
Net gain (loss) from asset sales, inclusive of restructuring costs			0.8
Minimum volume commitment			45.0
Minimum volume commitment remaining	$ 2.0		$ 2.0