Reinsurance and Other Monoline Exposures - Effect of Reinsurance on Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Premiums Written:
Direct	$ 57	$ 46	$ 192	$ 227
Assumed	(7)	(1)	324	8
Ceded	1	27	14	37
Net	51	72	530	272
Premiums Earned:
Direct	127	186	400	516
Assumed	19	6	33	20
Ceded	(4)	(6)	(10)	(24)
Net	142	186	423	512
Loss and LAE:
Direct	18	231	53	377
Assumed	1	(1)	(7)	(1)
Ceded	(2)	(7)	(3)	(22)
Net	$ 17	$ 223	$ 43	$ 354