v3.5.0.2
Derivative Instruments (Details 4) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Power contracts included in operating revenues $ 2,355 $ 1,948 $ 5,134 $ 5,036
Natural gas contracts included in fuel and purchased energy expense 1,472 1,073 3,140 2,849
Interest expense 158 159 472 471
Gain (Loss) on Derivative Instruments, Net, Pretax 141 86 192 319
Gain (Loss) on Sale of Derivatives [1],[2] 32 160 213 323
Mark-to-market gain (loss) [3] 109 (74) (21) (4)
Power [Member]        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Power contracts included in operating revenues [1],[2] 308 189 240 423
Interest Rate Contract [Member]        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Interest expense [3] 0 1 1 2
Mark-to-market gain (loss) [3] 0 1 1 2
Energy Related Derivative [Member]        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Gain (Loss) on Sale of Derivatives [1],[2] 32 160 213 323
Mark-to-market gain (loss) [3] 109 (75) (22) (6)
Natural Gas [Member]        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Natural gas contracts included in fuel and purchased energy expense [1],[2] $ (167) $ (104) $ (49) $ (106)
[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 de-designation of interest rate swap cash flow hedges and related reclassification of AOCI into earnings, hedge ineffectiveness and adjustments to reflect changes in credit default risk exposure.