Derivative Financial Instruments (Derivatives That Qualify For Regulatory Deferral) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral	$ 51	$ (61)
Fuel Oils [Member]
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral		14	[1]
Natural Gas [Member]
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral	(26)	(91)
Power [Member]
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral	80	12
Uranium [Member]
Derivative [Line Items]
Net change in market value of derivatives that qualify for regulatory deferral	$ (3)	$ 4

[1] Includes amounts for intercompany eliminations.