Derivative Instruments, Hedging Activities and Fair Value Measurements, Liability Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Interest rate derivatives [Member]
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	$ 16.3	$ 3.7
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Amounts of Liabilities Presented in the Balance Sheet	16.3	3.7
Financial Instruments	(2.1)	(3.2)
Cash Collateral Paid	0.0	0.0
Amounts That Would Have Been Presented On Net Basis	14.2	0.5
Commodity derivatives [Member]
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	475.4	143.0
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Amounts of Liabilities Presented in the Balance Sheet	475.4	143.0
Financial Instruments	(244.1)	(143.0)
Cash Collateral Paid	(231.3)	0.0
Amounts That Would Have Been Presented On Net Basis	$ 0.0	$ 0.0