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
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Total premiums earned	$ 93	$ 131
United States [Member]
Segment Reporting Information [Line Items]
Total premiums earned	67	106
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	9	8
Europe Excluding United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	3	3
Internationally Diversified [Member]
Segment Reporting Information [Line Items]
Total premiums earned	2	3
Central And South America [Member]
Segment Reporting Information [Line Items]
Total premiums earned	9	8
Asia [Member]
Segment Reporting Information [Line Items]
Total premiums earned	1	1
Other [Member]
Segment Reporting Information [Line Items]
Total premiums earned	$ 2	$ 2