Investments (Recorded Other-Than-Temporary Impairment Losses on Investments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Investments, Debt and Equity Securities [Abstract]
Total other-than-temporary impairment losses	$ 75	[1]	$ 59	[1]	$ 175	[1]
Losses recorded to decommissioning trust regulatory liability	(24)		(21)		(80)
Losses recognized in other comprehensive income (before taxes)	(3)		(3)		(3)
Net impairment losses recognized in earnings	48		35		92
Other-than-temporary impairment losses for debt securities	$ 6		$ 10		$ 13

[1] Amounts include other-than-temporary impairment losses for debt securities of $6 million, $10 million and $13 million at December 31, 2011, 2010 and 2009, respectively.