v2.3.0.11
Fair Value Disclosures (Fair Value of Financial Assets and Liabilities Measured on a Recurring Basis) (Details) (USD $)
In Millions
Jun. 30, 2011
Dec. 31, 2010
Available-for-sale securities $ 81.2 $ 81.4
Fair value assets measured on recurring basis, total 387.8 481.2
Fair value liabilities measured on recurring basis, total 262.8 355.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
    
Available-for-sale securities 38.8 43.5
Fair value assets measured on recurring basis, total 159.9 217.3
Fair value liabilities measured on recurring basis, total 257.1 348.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Financial Price Risk Programs [Member]
    
Fair Value assets measured on recurring basis, derivative financial instruments 121.1 173.8
Fair value liabilities measured on recurring basis, derivative financial instruments 257.1 348.5
Significant Other Observable Inputs (Level 2) [Member]
    
Available-for-sale securities 42.4 37.9
Fair value assets measured on recurring basis, total 227.9 263.6
Fair value liabilities measured on recurring basis, total 4.9 6.9
Significant Other Observable Inputs (Level 2) [Member] | Physical Price Risk Programs [Member]
    
Fair Value assets measured on recurring basis, derivative financial instruments 122.3 161.4
Fair value liabilities measured on recurring basis, derivative financial instruments 2.8 3.6
Significant Other Observable Inputs (Level 2) [Member] | Financial Price Risk Programs [Member]
    
Fair Value assets measured on recurring basis, derivative financial instruments 2.5 3.2
Fair value liabilities measured on recurring basis, derivative financial instruments 2.1 3.3
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Risk Activities [Member]
    
Fair Value assets measured on recurring basis, derivative financial instruments 60.7 61.1
Significant Unobservable Inputs (Level 3) [Member]
    
Fair value assets measured on recurring basis, total   0.3
Fair value liabilities measured on recurring basis, total 0.8 0.1
Significant Unobservable Inputs (Level 3) [Member] | Financial Price Risk Programs [Member]
    
Fair Value assets measured on recurring basis, derivative financial instruments   0.3
Fair value liabilities measured on recurring basis, derivative financial instruments 0.8 0.1
Physical Price Risk Programs [Member]
    
Fair Value assets measured on recurring basis, derivative financial instruments 122.3 161.4
Fair value liabilities measured on recurring basis, derivative financial instruments 2.8 3.6
Financial Price Risk Programs [Member]
    
Fair Value assets measured on recurring basis, derivative financial instruments 123.6 177.3
Fair value liabilities measured on recurring basis, derivative financial instruments 260.0 351.9
Interest Rate Risk Activities [Member]
    
Fair Value assets measured on recurring basis, derivative financial instruments $ 60.7 $ 61.1