Fair Value Measurements (Details 3) (Commodity contracts, USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Revenue
 
Change in fair value of assets and liabilities measured on recurring basis, utilized Level 3 inputs  
Beginning of Period $ 4.2
Total Gains (Losses) Included in Earnings 0.8
Settlements 3.7
End of Period 1.3
Change in Unrealized Gains Relating to Assets (Liabilities) that are Held at end of Period (0.4)
Cost of revenue.
 
Change in fair value of assets and liabilities measured on recurring basis, utilized Level 3 inputs  
Beginning of Period 1.3
Total Gains (Losses) Included in Earnings 0.5
Settlements 0.5
End of Period 0.3
Change in Unrealized Gains Relating to Assets (Liabilities) that are Held at end of Period $ 0.8