Reinsurance and Other Monoline Exposures - Effect of Reinsurance on Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Premiums Written:
Direct	$ 62	$ 72	$ 135	$ 181
Assumed	331	7	331	9
Ceded	24	(1)	13	10
Net	417	78	479	200
Premiums Earned:
Direct	130	163	273	330
Assumed	9	8	14	14
Ceded	(3)	(9)	(6)	(18)
Net	136	162	281	326
Loss and LAE:
Direct	49	79	35	146
Assumed	(5)	(3)	(8)	0
Ceded	0	(4)	(1)	(15)
Net	$ 44	$ 72	$ 26	$ 131