Derivative Contracts Schedule of Derivatives Financial Statement Presentation (Details) - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 8.3	$ 171.0
Derivative Liability, Fair Value, Gross	86.6	5.8
Short-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7.7	147.8
Derivative Liability, Fair Value, Gross	52.9	1.8
Long-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.6	23.2
Derivative Liability, Fair Value, Gross	33.7	4.0
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	8.3	171.0
Derivative Liability, Fair Value, Gross	86.6	5.8
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | Short-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7.7	147.8
Derivative Liability, Fair Value, Gross	52.9	1.8
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | Long-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.6	23.2
Derivative Liability, Fair Value, Gross	$ 33.7	$ 4.0