Investments (Selected Information Regarding Marketable Equity and Debt Securities) (Details) (USD $) In Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Available-for-sale securities:
Proceeds from sales	$ 437		$ 627		$ 939		$ 1,140
Realized gains	18	[1]	17	[1]	32	[1]	73	[1]
Realized losses	$ 12	[1]	$ 28	[1]	$ 20	[1]	$ 54	[1]

[1] Includes realized gains or losses recorded to the decommissioning trust regulatory liability.