v3.5.0.2
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Dec. 31, 2014
Fair Value Measurement [Domain]            
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]            
Cash and Cash Equivalents, at Carrying Value $ 215   $ 215   $ 906  
Restricted Cash and Cash Equivalents 168   168   228  
Balance, beginning of period (65) $ 203 (46) $ 85    
Included in operating revenues [1] (174) 45 (181) 176    
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Gain (Loss) Included In Fuel And Purchased Energy Expense [2] 165 0 155 2    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 4 2 5 4    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements (1) (10) (4) (21)    
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] 8 3 8 (3)    
Balance, end of period (63) 243 (63) 243    
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) (9) 45 (26) 178    
Cash and Cash Equivalents, at Carrying Value 215 $ 422 215 $ 422 906 $ 717
Restricted Cash and Cash Equivalents $ 168   $ 168   $ 228  
[1] For power contracts and other power-related products, included on our Consolidated Condensed Statements of Operations.
[2] For natural gas and power 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 six months ended June 30, 2016 and 2015.
[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 six months ended June 30, 2016 and 2015.
[5] We had $(8) million and $(3) million in losses transferred out of level 3 into level 2 for the three months ended June 30, 2016 and 2015, respectively, and $(8) million in losses and $3 million in gains transferred out of level 3 into level 2 for the six months ended June 30, 2016 and 2015, respectively, due to changes in market liquidity in various power markets.