v2.4.0.8
Derivative Instruments (Details 3) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Summary of Derivative Instruments by Risk Exposure [Abstract]    
Power contracts included in operating revenues $ (237) $ (74)
Natural gas contracts included in fuel and purchased energy expense 125 45
Interest rate swaps included in interest expense 1 2
Gain (Loss) on Derivative Instruments, Net, Pretax (111) (27)
Gain (Loss) on Sale of Derivatives (39) [1] 28 [1]
Unrealized gain (loss) (72) [2] (55) [2]
Interest Rate Swap [Member]
    
Summary of Derivative Instruments by Risk Exposure [Abstract]    
Unrealized gain (loss) 1 [2] 2 [2]
Commodity Option [Member]
    
Summary of Derivative Instruments by Risk Exposure [Abstract]    
Gain (Loss) on Sale of Derivatives (39) [1] 28 [1]
Unrealized gain (loss) $ (73) [2] $ (57) [2]
[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 unrealized 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.