Derivative Contracts Schedule of Derivatives Financial Statement Presentation (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative instruments - assets	$ 170.0	$ 348.9
Derivative instruments - liabilities	4.8	0.0
Commodity Contract [Member] | Short term [Member]
Derivative [Line Items]
Derivative instruments - assets	146.8	339.0
Derivative instruments - liabilities	0.8	0.0
Commodity Contract [Member] | Long term [Member]
Derivative [Line Items]
Derivative instruments - assets	23.2	9.9
Derivative instruments - liabilities	4.0
Fair Value, Inputs, Level 2 [Member]
Derivative [Line Items]
Derivative instruments - assets	171.0	349.2
Derivative instruments - liabilities	5.8	0.3
Fair Value, Inputs, Level 2 [Member] | Commodity Contract [Member] | Short term [Member]
Derivative [Line Items]
Derivative instruments - assets	147.8	339.3
Derivative instruments - liabilities	1.8	0.3
Fair Value, Inputs, Level 2 [Member] | Commodity Contract [Member] | Long term [Member]
Derivative [Line Items]
Derivative instruments - assets	23.2	9.9
Derivative instruments - liabilities	$ 4.0	$ 0.0