Investments (Selected Information Regarding Marketable Equity and Debt Securities) (Details) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Available-for-sale securities:
Proceeds from sales	$ 465		$ 398		$ 1,404		$ 1,538
Realized gains	23	[1]	16	[1]	55	[1]	89	[1]
Realized losses	$ 62	[1]	$ 4	[1]	$ 82	[1]	$ 58	[1]

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