v3.4.0.3
Derivative Instruments (Details 3) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Summary of Derivative Instruments by Risk Exposure [Abstract]    
Power contracts included in operating revenues $ 1,615 $ 1,646
Natural gas contracts included in fuel and purchased energy expense 1,126 1,010
Interest expense 157 154
Gain (Loss) on Derivative Instruments, Net, Pretax 24 130
Gain (Loss) on Sale of Derivatives [1],[2] 118 59
Mark-to-market gain (loss) [3] (94) 71
Power [Member]    
Summary of Derivative Instruments by Risk Exposure [Abstract]    
Power contracts included in operating revenues [1] 204 119
Interest Rate Swap [Member]    
Summary of Derivative Instruments by Risk Exposure [Abstract]    
Interest expense 1 1
Mark-to-market gain (loss) [3] 1 1
Energy Related Derivative [Member]    
Summary of Derivative Instruments by Risk Exposure [Abstract]    
Gain (Loss) on Sale of Derivatives [1],[2] 118 59
Mark-to-market gain (loss) [3] (95) 70
Natural Gas [Member]    
Summary of Derivative Instruments by Risk Exposure [Abstract]    
Natural gas contracts included in fuel and purchased energy expense [1] $ (181) $ 10
[1] Does not include the realized value associated with derivative instruments that settle through physical delivery.
[2] Includes amortization of acquisition date fair value of derivative activity related to the acquisition of Champion Energy.
[3] In addition to changes in market value on derivatives not designated as hedges, changes in mark-to-market gain (loss) also includes hedge ineffectiveness and adjustments to reflect changes in credit default risk exposure.