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, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total premiums earned	$ 53	$ 75	$ 73
United States [Member]
Segment Reporting Information [Line Items]
Total premiums earned	45	45	55
Other Americas [Member]
Segment Reporting Information [Line Items]
Total premiums earned	8	29	16
Other [Member]
Segment Reporting Information [Line Items]
Total premiums earned	$ 0	$ 1	$ 2