v3.3.0.814
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Dec. 31, 2013
Fair Value Measurement [Domain]            
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]            
Cash and Cash Equivalents, at Carrying Value $ 624   $ 624   $ 679  
Restricted Cash and Cash Equivalents 250   250   217  
Balance, beginning of period 243 $ (9) 85 $ 14    
Included in operating revenues [1] 70 7 236 (1)    
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Gain (Loss) Included In Fuel And Purchased Energy Expense [2] (2) 5 (2) 9    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 0 0 3 1    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements (8) 9 (24) (7)    
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount 0 0 0 0    
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount 0 0 0 0    
Transfers into level 3 [3],[4] 0 0 0 0    
Transfers out of Level 3 [4],[5] (11) (1) (6) (5)    
Balance, end of period 292 11 292 11    
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 68 12 234 8    
Cash and Cash Equivalents, at Carrying Value 659 $ 1,529 659 $ 1,529 717 $ 941
Restricted Cash and Cash Equivalents $ 275   $ 275   $ 244  
[1] For power contracts and other power-related products, 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 each of the three and nine months ended September 30, 2015 and 2014.
[4] 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, 2015 and 2014.
[5] We had $11 million and $1 million in gains transferred out of level 3 into level 2 for the three months ended September 30, 2015 and 2014, respectively, and $6 million and $5 million in gains transferred out of level 3 into level 2 for the nine months ended September 30, 2015 and 2014, respectively, due to changes in market liquidity in various power markets.