Derivative Financial Instruments (Derivatives That Qualify For Regulatory Deferral) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral	$ (175)	[1]	$ 61	[1]
Fuel Oils [Member]
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral	5	[1]	29	[1]
Natural Gas [Member]
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral	(18)	[1]	31	[1]
Power [Member]
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral	(162)	[1]	2	[1]
Uranium [Member]
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral			$ (1)	[1]

[1] Includes amounts for intercompany eliminations.