Business Segments (Summary Of Premiums Earned On Financial Guarantees And Insured Derivatives By Geographic Location Of Risk) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Total premiums earned	$ 112	$ 168	$ 377	$ 506
United States [Member]
Segment Reporting Information [Line Items]
Total premiums earned	82	141	297	402
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	9	9	26	27
Europe Excluding United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	3	3	9	12
Internationally Diversified [Member]
Segment Reporting Information [Line Items]
Total premiums earned	2	3	8	13
Central And South America [Member]
Segment Reporting Information [Line Items]
Total premiums earned	13	8	28	40
Asia [Member]
Segment Reporting Information [Line Items]
Total premiums earned	1	2	3	4
Other [Member]
Segment Reporting Information [Line Items]
Total premiums earned	$ 2	$ 2	$ 6	$ 8