Derivative Contracts Schedule of Derivatives Financial Statement Presentation (Details) - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 7.6	$ 171.0
Derivative Liability, Fair Value, Gross	61.0	5.8
Short-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7.6	147.8
Derivative Liability, Fair Value, Gross	41.6	1.8
Long-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		23.2
Derivative Liability, Fair Value, Gross	19.4	4.0
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7.6	171.0
Derivative Liability, Fair Value, Gross	61.0	5.8
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | Short-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	7.6	147.8
Derivative Liability, Fair Value, Gross	41.6	1.8
Fair Value, Measurements, Recurring [Member] | Commodity Contract [Member] | Long-term [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0.0	23.2
Derivative Liability, Fair Value, Gross	$ 19.4	$ 4.0