Derivative Contracts Schedule of Derivatives Financial Statement Presentation (Details) - Fair Value, Inputs, Level 2 [Member] - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 177.7	$ 349.2
Derivative Liability, Fair Value, Gross	10.6	0.3
Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	177.7	349.2
Derivative Liability, Fair Value, Gross	10.6	0.3
Commodity Contract [Member] | Short-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	170.7	339.3
Derivative Liability, Fair Value, Gross	8.1	0.3
Commodity Contract [Member] | Long-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7.0	9.9
Derivative Liability, Fair Value, Gross	$ 2.5	$ 0.0