Derivatives (Details 3) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Gain (loss) on derivative    
Gains or losses that were excluded from the assessment of the effectiveness of fair value hedges $ 0 $ 0
Derivatives designated as hedging instruments | Fair value hedges | Commodity contracts | Cost of revenue.    
Gain (loss) on derivative    
Realized and Unrealized Gain (Loss) on Hedge 4,000,000 400,000
Realized and Unrealized Gain (Loss) on Hedged Item (500,000) (7,600,000)
Derivatives not designated as hedging instruments    
Gain (loss) on derivative    
Realized and Unrealized Gain (Loss) 22,000,000 15,500,000
Derivatives not designated as hedging instruments | Commodity contracts | Revenue    
Gain (loss) on derivative    
Realized and Unrealized Gain (Loss) 20,600,000 6,900,000
Derivatives not designated as hedging instruments | Commodity contracts | Cost of revenue.    
Gain (loss) on derivative    
Realized and Unrealized Gain (Loss) (11,700,000) 9,600,000
Derivatives not designated as hedging instruments | Foreign currency contracts | Revenue    
Gain (loss) on derivative    
Realized and Unrealized Gain (Loss) 3,900,000 (300,000)
Derivatives not designated as hedging instruments | Foreign currency contracts | Other income (expense), net    
Gain (loss) on derivative    
Realized and Unrealized Gain (Loss) $ 9,200,000 $ (700,000)