Insurance In Force (Summary Of Components Of Financial Guarantee Net Premiums Earned, Including Premiums Assumed From And Ceded To Other Companies) (Detail) (Non Variable Interest Entities [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Non Variable Interest Entities [Member]
Direct	$ 489	$ 505	$ 516
Assumed	130	112	106
Gross	619	617	622
Ceded	(14)	(12)	(28)
Premiums earned (net of ceded premiums of $14, $12 and $28)	$ 605	$ 605	$ 594