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Risk Management Activities (Location And Fair Value Of Derivative Instruments On Consolidated Balance Sheets) (Details) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2013
Dec. 31, 2012
Derivatives, Fair Value [Line Items]    
Total Asset Derivatives $ 73.5 $ 148.2
Total Liability Derivatives 52.5 115.5
Designated As Hedging Instruments [Member] | Interest Rate Risk Activities [Member]
   
Derivatives, Fair Value [Line Items]    
Total Asset Derivatives 30.9 40.4
Designated As Hedging Instruments [Member] | Interest Rate Risk Activities [Member] | Price Risk Management Assets (Current) [Member]
   
Derivatives, Fair Value [Line Items]    
Total Asset Derivatives 0 0
Designated As Hedging Instruments [Member] | Interest Rate Risk Activities [Member] | Price Risk Management Assets (Noncurrent) [Member]
   
Derivatives, Fair Value [Line Items]    
Total Asset Derivatives 30.9 40.4
Designated As Hedging Instruments [Member] | Commodity Price Risk Programs [Member]
   
Derivatives, Fair Value [Line Items]    
Total Liability Derivatives 0 0.1
Designated As Hedging Instruments [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Current) [Member]
   
Derivatives, Fair Value [Line Items]    
Total Liability Derivatives 0 0.1
Designated As Hedging Instruments [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Noncurrent) [Member]
   
Derivatives, Fair Value [Line Items]    
Total Liability Derivatives 0 0
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member]
   
Derivatives, Fair Value [Line Items]    
Total Asset Derivatives 42.6 107.8
Total Liability Derivatives 52.5 115.4
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Assets (Current) [Member]
   
Derivatives, Fair Value [Line Items]    
Total Asset Derivatives 39.6 92.2
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Assets (Noncurrent) [Member]
   
Derivatives, Fair Value [Line Items]    
Total Asset Derivatives 3.0 15.6
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Current) [Member]
   
Derivatives, Fair Value [Line Items]    
Total Liability Derivatives 47.5 95.1
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Noncurrent) [Member]
   
Derivatives, Fair Value [Line Items]    
Total Liability Derivatives $ 5.0 $ 20.3