Derivative Contracts Schedule of Derivatives Financial Statement Presentation (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Inputs, Level 2 [Member]
Derivative [Line Items]
Derivative instruments - assets	$ 1.7	$ 123.6
Derivative instruments - liabilities	19.2	1.1
Fair Value, Inputs, Level 2 [Member] | Short term [Member]
Derivative [Line Items]
Derivative instruments - assets	1.5	88.2
Derivative instruments - liabilities	18.7	0.4
Fair Value, Inputs, Level 2 [Member] | Long term [Member]
Derivative [Line Items]
Derivative instruments - assets	0.2	35.4
Derivative instruments - liabilities	0.5	0.7
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative [Line Items]
Derivative instruments - assets	1.7	123.6
Derivative instruments - liabilities	19.2	1.1
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | Short term [Member]
Derivative [Line Items]
Derivative instruments - assets	1.5	88.2
Derivative instruments - liabilities	18.7	0.4
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | Long term [Member]
Derivative [Line Items]
Derivative instruments - assets	0.2	35.4
Derivative instruments - liabilities	$ 0.5	0.7
Haynesville Divestiture [Member]
Derivative [Line Items]
Derivative instruments - assets		$ 0.3