Hedging Activities and Fair Value Measurements, Asset Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Interest rate derivatives [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	$ 12.4
Gross Amounts Offset in the Balance Sheet	0.0
Amounts of Assets Presented in the Balance Sheet	12.4
Financial Instruments	0.0
Cash Collateral Paid	0.0
Cash Collateral Received	0.0
Amounts That Would Have Been Presented On Net Basis	12.4
Commodity Derivatives [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	229.2	$ 127.8
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Amounts of Assets Presented in the Balance Sheet	229.2	127.8
Financial Instruments	(228.5)	(115.3)
Cash Collateral Paid	0.0	(11.0)
Cash Collateral Received	0.0	0.0
Amounts That Would Have Been Presented On Net Basis	$ 0.7	$ 1.5