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Fair Value Disclosures (Tables)
3 Months Ended
Mar. 31, 2012
Fair Value Disclosures [Abstract]  
Fair Value Of Financial Assets And Liabilities Measured On A Recurring Basis
Fair Value Of Financial Instruments Using Unobservable Inputs (Level 3)

Type of Instrument

   Fair Value at
March 31, 2012
     Valuation Technique    Unobservable Input    Range  
     (millions of dollars)                   

Natural Gas Options

   $ 12       Option model    Volatility Factor      0.60 – 2.03   

Natural Gas Physical Basis Contracts

   $ 2       Market comparable    Congestion adder    $ 0.02 – $0.43   
Reconciliations Of Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Gains Or (Losses) On Level 3 Instruments Included In Income
     Three Months Ended March 31,  
     2012      2011  
     (millions of dollars)  

Total net gains included in income for the period

   $ 1      $ 3  
  

 

 

    

 

 

 

Change in unrealized gains relating to assets still held at reporting date

   $ 1      $ 1  
  

 

 

    

 

 

 
Fair Value Of Financial Liabilities Measured On A Recurring Basis
Estimated Fair Values Of Debt And Equity Instruments
     December 31, 2011  
     Carrying
Amount
     Fair
Value
 
     (millions of dollars)  

Long-term debt

   $ 3,867      $ 4,577  

Transition Bonds issued by ACE Funding

     332        380  

Long-term project funding

     15        15