v3.7.0.1
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Dec. 31, 2015
Fair Value Measurement [Domain]            
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]            
Cash and Cash Equivalents, at Carrying Value $ 29   $ 29   $ 26  
Restricted Cash and Cash Equivalents 99   99   127  
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs 342 $ (65) 399 $ (46)    
Included in operating revenues [1] 28 (174) 104 (181)    
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Gain (Loss) Included In Fuel And Purchased Energy Expense [2] (14) 165 1 155    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases 3 4 3 5    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements (67) (1) (97) (4)    
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] (2) 0 3 0    
Transfers out of Level 3 [4],[5] 0 8 (113) 8    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs 294 (63) 294 (63)    
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 14 (9) 105 (26)    
Cash and Cash Equivalents, at Carrying Value 294 $ 215 294 $ 215 418 $ 906
Restricted Cash and Cash Equivalents $ 133   $ 133   $ 188  
[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 $(2) million and nil in gains transferred out of level 2 into level 3 for each of the three months ended June 30, 2017 and 2016, and $3 million and nil in losses transferred out of level 2 into level 3 for the six months ended June 30, 2017 and 2016, respectively, due to changes in market liquidity in various power markets.
[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, 2017 and 2016.
[5] We had nil and $(8) million in losses transferred out of level 3 into level 2 for the three months ended June 30, 2017 and 2016, respectively, and $113 million in gains and $(8) million in losses transferred out of level 3 into level 2 for the six months ended June 30, 2017 and 2016, respectively, due to changes in market liquidity in various power markets.