Business Segments (Summary Of Premiums Earned On Financial Guarantees And Insured Derivatives By Geographic Location Of Risk) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Total premiums earned	$ 90	$ 122	$ 288	$ 308
United States [Member]
Segment Reporting Information [Line Items]
Total premiums earned	71	78	232	216
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	8	9	23	28
Europe Excluding United Kingdom [Member]
Segment Reporting Information [Line Items]
Total premiums earned	2	2	4	6
Internationally Diversified [Member]
Segment Reporting Information [Line Items]
Total premiums earned	1	4	3	7
Central And South America [Member]
Segment Reporting Information [Line Items]
Total premiums earned	7	26	20	42
Asia [Member]
Segment Reporting Information [Line Items]
Total premiums earned	0	1	2	3
Other [Member]
Segment Reporting Information [Line Items]
Total premiums earned	$ 1	$ 2	$ 4	$ 6