v2.4.0.8
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]          
Balance, beginning of period $ 13 $ (10) $ 16 $ 17  
Included in net income:          
Included in operating revenues 7 [1] 1 [1] 8 [1] 3 [1]  
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Gain (Loss) Included In Fuel And Purchased Energy Expense 1 [2] 1 [2] 0 [2] 1 [2]  
Included in OCI 0 0 0 1  
Purchases, issuances and settlements:          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 0 0 0 0  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issues 0 (1) 0 (1)  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements (5) 25 (8) (4)  
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount 0 0 0 0  
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount 0 0 0 0  
Transfers into level 3 0 [3],[4] 0 [3],[4] 0 [3],[4] 0 [3],[4]  
Transfers out of Level 3 0 [3],[5] 0 [3],[5] 0 [3],[5] 1 [3],[5]  
Balance, end of period 16 16 16 16  
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Change in Unrealized Gain (Loss) Held At Period End 8 2 8 4  
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) [Abstract]          
Cash Equivalents Included In Cash And Cash Equivalents, Fair Value Disclosure 1,002   1,002   1,274
Cash Equivalents Included In Restricted Cash, Fair Value Disclosure $ 220   $ 220   $ 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] We transfer amounts among levels of the fair value hierarchy as of the end of each period. There were no transfers into or out of level 1 for each of the three and nine months ended September 30, 2013 and 2012.
[4] There were no transfers out of level 2 into level 3 for each of the three and nine months ended September 30, 2013 and 2012.
[5] There were no transfers out of level 3 into level 2 for the three and nine months ended September 30, 2013. We had nil and $1 million in gains transferred out of level 3 into level 2 for the three and nine months ended September 30, 2012, respectively, due to changes in market liquidity in various power markets.