Derivatives (Details 2) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset $ 603.6 $ 695.3
Derivative liability 573.0 649.6
Derivative, credit-risk related contingent features    
Net liability position 73.3 111.7
Collateral posted 57.5 89.4
Additional assets required to be posted should credit-risk contingent feature be triggered 15.8 22.3
Derivatives designated as hedging instruments    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 11.8 23.5
Derivative liability 5.2 1.7
Derivatives designated as hedging instruments | Commodity contracts | Other current assets    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 9.0 18.8
Derivative liability 4.8 1.0
Derivatives designated as hedging instruments | Commodity contracts | Accrued expenses and other current liabilities    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 2.8 4.7
Derivative liability 0.4 0.7
Derivatives not designated as hedging instruments    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 591.8 671.8
Derivative liability 567.8 647.9
Derivatives not designated as hedging instruments | Commodity contracts | Other current assets    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 355.3 399.0
Derivative liability 106.1 76.0
Derivatives not designated as hedging instruments | Commodity contracts | Identifiable intangible and other non-current assets    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 14.1 12.1
Derivative liability 0.5 0.6
Derivatives not designated as hedging instruments | Commodity contracts | Accrued expenses and other current liabilities    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 198.8 234.1
Derivative liability 439.0 530.0
Derivatives not designated as hedging instruments | Commodity contracts | Other long-term liabilities    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 6.0 4.8
Derivative liability 17.1 29.3
Derivatives not designated as hedging instruments | Foreign currency contracts | Other current assets    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset 16.6 21.3
Derivative liability 5.1 12.0
Derivatives not designated as hedging instruments | Foreign currency contracts | Identifiable intangible and other non-current assets    
Information about derivative instruments measured at fair value and their locations on the consolidated balance sheet    
Derivative asset $ 1.0 $ 0.5