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, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Total premiums earned	$ 37	$ 53	$ 75
United States [Member]
Segment Reporting Information [Line Items]
Total premiums earned	29	45	45
Other Americas [Member]
Segment Reporting Information [Line Items]
Total premiums earned	8	8	29
Other [Member]
Segment Reporting Information [Line Items]
Total premiums earned	$ 0	$ 0	$ 1