Financial Guarantee Insurance Contracts - Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Written	$ (2)	$ 1	$ 28
Assumed Reinsurance Premiums Written	0	0	0
Ceded Reinsurance Premiums Written	(35)	1	(31)
Premiums written, net of reinsurance	33	0	60
Direct Premiums Earned	62	65	75
Premiums Earned, Net	47	54	66
Assumed Reinsurance Premiums Earned	0	1	0
Ceded Reinsurance Premiums Earned	15	12	10
Reinsurance on premiums earned, Net	47	54	$ 66
Reinsurance Recoverable, Allowance for Credit Loss	$ 0	$ 0