v2.4.0.6
Derivative Instruments (Details 3) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Power contracts included in operating revenues $ (272) $ 48 $ (180) $ (9)
Natural gas contracts included in fuel and purchased energy expense 20 20 124 22
Interest rate swaps included in interest expense 3 1 6 2
Gain (Loss) on interest rate derivatives, net 0 37 14 146
Gain (Loss) on Derivative Instruments, Net, Pretax (249) [1] 32 [1] (64) [1] (131) [1]
Gain (Loss) on Sale of Derivatives 94 (18) 55 (54)
Unrealized gain (loss) (343) [1] 50 [1] (119) [1] (77) [1]
Interest Rate Swap [Member]
        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Gain (Loss) on Sale of Derivatives 0 (60) (157) (106)
Unrealized gain (loss) 3 [1] 24 [1] 149 [1] (38) [1]
Commodity Option [Member]
        
Summary of Derivative Instruments by Risk Exposure [Abstract]        
Gain (Loss) on Sale of Derivatives 94 42 212 52
Unrealized gain (loss) $ (346) [1] $ 26 [1] $ (268) [1] $ (39) [1]
[1] 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 income, hedge ineffectiveness and adjustments to reflect changes in credit default risk exposure