Derivative Financial Instruments (Derivatives that Qualify for Regulatory Deferral) (Details) (USD $) In Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	$ 75	[1]	$ 48	[1]	$ 136	[1]	$ (68)	[1]
Heating Oil [Member]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	(13)	[1]	(9)	[1]	16	[1]	(8)	[1]
Natural Gas (Generation) [Member]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	3	[1]	25	[1]	34	[1]	(81)	[1]
Power [Member]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	88	[1]	33	[1]	90	[1]	23	[1]
Uranium [Member]
Amount Gain Loss On Derivative Instruments That Qualify For Regulatory Deferral Net	$ (3)	[1]	$ (1)	[1]	$ (4)	[1]	$ (2)	[1]

[1] Includes amounts for intercompany eliminations.