Business Segments (Summary Of Premiums Earned On Financial Guarantees And Insured Derivatives By Geographic Location Of Risk) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total premiums earned	$ 75	$ 73	$ 85
United States [Member]
Segment Reporting Information [Line Items]
Total premiums earned	45	55	63
Other Americas [Member]
Segment Reporting Information [Line Items]
Total premiums earned	29	16	17
Other [Member]
Segment Reporting Information [Line Items]
Total premiums earned	$ 1	$ 2	$ 5