Acquisitions & Divestitures Pinedale Divestiture (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Divestitures [Line Items]
Proceeds from disposition of assets			$ 217.5	$ 787.9
Net gain (loss) from asset sales, inclusive of restructuring costs	$ 27.1	$ 185.4	26.7	205.2
Income (loss) before income taxes	9.8	(6.5)	(499.9)	188.7
Pinedale Divestiture [Member]
Divestitures [Line Items]
Proceeds from disposition of assets		718.2
Net gain (loss) from asset sales, inclusive of restructuring costs			1.2
Income (loss) before income taxes		$ 208.2		$ 251.2
Minimum volume commitment			45.0
Minimum volume commitment remaining	$ 23.0		$ 23.0