Investments (Recorded Other-Than-Temporary Impairment Losses on Investments) (Details) (USD $) In Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Investments
Total other-than-temporary impairment losses	$ 10	[1]	$ 41	[1]	$ 15	[1]	$ 48	[1]
Losses recorded to decommissioning trust regulatory liability	(4)		(13)		(6)		(16)
Losses recognized in other comprehensive income (before taxes)	(1)		(1)		(1)		(2)
Net impairment losses recognized in earnings	5		27		8		30
Other-than-temporary impairment losses for debt securities	$ 1		$ 1		$ 2		$ 3

[1] Amount includes other-than-temporary impairment losses for debt securities of $1 million for the three months ended June 30, 2011 and 2010, and $2 million and $3 million for the six months ended June 30, 2011 and 2010, respectively.