Financial Guarantee Insurance Contracts - Effect of Reinsurance on Premiums Written and Earned (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Written	$ (3)	$ (1)	$ (5)	$ 10
Assumed Reinsurance Premiums Written	0	0	0	0
Ceded Reinsurance Premiums Written	9	0	16	(1)
Premiums written, net of reinsurance	13	0	21	(11)
Direct Premiums Earned	14	14	31	27
Assumed Reinsurance Premiums Earned	0	0	0	1
Ceded Reinsurance Premiums Earned	3	3	6	6
Reinsurance on premiums earned, Net	$ 11	$ 11	$ 25	$ 21