Derivative Financial Instruments (Derivatives That Qualify For Regulatory Deferral) (Details) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Derivative [Line Items]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	$ (17)	[1]	$ (55)	[1]	$ 119	[1]	$ (123)	[1]
Heating Oil [Member]
Derivative [Line Items]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	(20)	[1]	10	[1]	(4)	[1]	2	[1]
Natural Gas (Generation) [Member]
Derivative [Line Items]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	(11)	[1]	(46)	[1]	23	[1]	(127)	[1]
Power [Member]
Derivative [Line Items]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	13	[1]	(21)	[1]	103	[1]	2	[1]
Uranium [Member]
Derivative [Line Items]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	$ 1	[1]	$ 2	[1]	$ (3)	[1]

[1] Includes amounts for intercompany eliminations.