v3.3.0.814
Derivative Instruments (Details 3) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Power contracts included in operating revenues $ 1,948 $ 2,187 $ 5,036 $ 6,091
Natural gas contracts included in fuel and purchased energy expense 1,073 1,268 2,849 3,759
Interest expense 159 156 471 491
Gain (Loss) on Derivative Instruments, Net, Pretax 86 77 319 126
Gain (Loss) on Sale of Derivatives [1] 160 59 323 38
Mark-to-market gain (loss) [2] (74) 18 (4) 88
Power [Member]        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Power contracts included in operating revenues 189 53 423 (26)
Interest Rate Swap [Member]        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Interest expense 1 7 2 9
Mark-to-market gain (loss) [2] 1 7 2 9
Energy Related Derivative [Member]        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Gain (Loss) on Sale of Derivatives [1] 160 59 323 38
Mark-to-market gain (loss) [2] (75) 11 (6) 79
Natural Gas [Member]        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Natural gas contracts included in fuel and purchased energy expense $ (104) $ 17 $ (106) $ 143
[1] Does not include the realized value associated with derivative instruments that settle through physical delivery.
[2] In addition to changes in market value on derivatives not designated as hedges, changes in mark-to-market gain (loss) also includes de-designation of interest rate swap cash flow hedges and related reclassification from AOCI into earnings, hedge ineffectiveness and adjustments to reflect changes in credit default risk exposure.