Acquisitions & Divestitures Other Acquisitions (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Bargain purchase gain from acquisition	$ (0.4)	$ 4.4
Payments to acquire oil and gas property	94.5	39.9
Other Acquisitions [Member]
Business Acquisition [Line Items]
Bargain purchase gain from acquisition		4.4
Acquisition Costs, Period Cost	94.5	46.1
Goodwill	$ 5.3	3.7
Cash [Member] | Other Acquisitions [Member]
Business Acquisition [Line Items]
Payments to acquire oil and gas property		39.9
Accounts Receivable [Member] | Other Acquisitions [Member]
Business Acquisition [Line Items]
Payments to acquire oil and gas property		$ (6.2)