Derivative Instruments, Hedging Activities and Fair Value Measurements, Asset Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Interest rate derivatives [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	$ 5.7
Gross Amounts Offset in the Balance Sheet	0.0
Amounts of Assets Presented in the Balance Sheet	5.7
Financial Instruments	0.0
Cash Collateral Received	0.0
Cash Collateral Paid	0.0
Amounts That Would Have Been Presented On Net Basis	5.7
Commodity Derivatives [Member]
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	139.4	$ 127.8
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Amounts of Assets Presented in the Balance Sheet	139.4	127.8
Financial Instruments	(139.4)	(115.3)
Cash Collateral Received	0.0	0.0
Cash Collateral Paid	50.4	(11.0)
Amounts That Would Have Been Presented On Net Basis	$ 50.4	$ 1.5