Investments (Recorded Other-Than-Temporary Impairment Losses on Investments) (Details) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Investments, Debt and Equity Securities [Abstract]
Total other-than-temporary impairment losses	$ 54	[1]	$ 4	[1]	$ 69	[1]	$ 52	[1]
Losses recorded to decommissioning trust regulatory liability	(16)		(1)		(22)		(17)
Losses recognized in other comprehensive income (before taxes)	(2)		0		(3)		(2)
Net impairment losses recognized in earnings	36		3		44		33
Other-than-temporary impairment losses for debt securities	$ 3		$ 1		$ 5		$ 4

[1] Amount includes other-than-temporary impairment losses for debt securities of $3 million and $1 million for the three months ended September 30, 2011 and 2010, respectively, and $5 million and $4 million for the nine months ended September 30, 2011 and 2010, respectively.