Derivative Instruments, Hedging Activities and Fair Value Measurements, Liability Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Interest rate derivatives [Member]
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	$ 13.5
Gross Amounts Offset in the Balance Sheet	0.0
Amounts of Liabilities Presented in the Balance Sheet	13.5
Financial Instruments	0.0
Cash Collateral Paid	0.0
Amounts That Would Have Been Presented On Net Basis	13.5
Commodity Derivatives [Member]
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	116.2	$ 162.4
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Amounts of Liabilities Presented in the Balance Sheet	116.2	162.4
Financial Instruments	(115.3)	(158.6)
Cash Collateral Paid	0.0	(2.3)
Amounts That Would Have Been Presented On Net Basis	$ 0.9	$ 1.5