Acquisitions & Divestitures Pinedale Divestiture (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Divestitures [Line Items]
Proceeds from disposition of assets	$ 617.4	$ 33.3
Net gain (loss) from asset sales, inclusive of restructuring costs	(13.2)	3.5
Income (loss) before income taxes	(228.7)	$ (67.5)
Pinedale Divestiture [Member]
Divestitures [Line Items]
Proceeds from disposition of assets			$ 718.2
Net gain (loss) from asset sales, inclusive of restructuring costs	1.0
Minimum volume commitment	45.0
Minimum volume commitment remaining	$ 5.9