v2.4.0.6
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Balance, beginning of period $ 16 $ 17  
Included in net income:      
Included in operating revenues 1 [1] 10 [1]  
Included In Fuel And Purchased Energy Expense 0 [2] (4) [2]  
Included in OCI 0 4  
Purchases, issuances and settlements:      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 0 1  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issues 0 (1)  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements (3) (6)  
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount 0 0  
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount 0 0  
Transfers into level 3 0 [3] 0 [3]  
Transfers out of Level 3 (1) [4] (4) [4]  
Balance, end of period 13 17  
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Change in Unrealized Gain (Loss) Held At Period End 1 6  
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) [Abstract]      
Cash Equivalents Included In Cash And Cash Equivalents, Fair Value Disclosure 952   1,274
Cash Equivalents Included In Restricted Cash, Fair Value Disclosure $ 172   $ 228
[1] For power contracts and Heat Rate swaps and options, included on our Consolidated Condensed Statements of Operations.
[2] For natural gas contracts, swaps and options, included on our Consolidated Condensed Statements of Operations.
[3] There were no transfers out of level 2 into level 3 for the three months ended March 31, 2013 and 2012.
[4] We had $1 million and $4 million in gains transferred out of level 3 into level 2 for the three months ended March 31, 2013 and 2012, respectively, due to changes in market liquidity in various power markets.