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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Total premiums earned	$ 93	$ 134	$ 186	$ 265
United States [Member]
Segment Reporting Information [Line Items]
Total premiums earned	71	109	138	215
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	10	9	19	17
Europe Excluding United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	1	3	4	6
Internationally Diversified [Member]
Segment Reporting Information [Line Items]
Total premiums earned	1	3	3	6
Central And South America [Member]
Segment Reporting Information [Line Items]
Total premiums earned	7	7	16	15
Asia [Member]
Segment Reporting Information [Line Items]
Total premiums earned	1	1	2	2
Other [Member]
Segment Reporting Information [Line Items]
Total premiums earned	$ 2	$ 2	$ 4	$ 4