Business Segments (Summary Of Premiums Earned On Financial Guarantees And Insured Derivatives By Geographic Location Of Risk) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Total premiums earned	$ 494	$ 661	$ 708
United States [Member]
Segment Reporting Information [Line Items]
Total premiums earned	391	530	545
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	34	36	37
Europe Excluding United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	11	15	29
Internationally Diversified [Member]
Segment Reporting Information [Line Items]
Total premiums earned	9	16	33
Central And South America [Member]
Segment Reporting Information [Line Items]
Total premiums earned	36	48	36
Asia [Member]
Segment Reporting Information [Line Items]
Total premiums earned	4	5	15
Other [Member]
Segment Reporting Information [Line Items]
Total premiums earned	$ 9	$ 11	$ 13