Reinsurance - Effect of Reinsurance on Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Premiums Written:
Direct									$ 288	$ 297	$ 165
Assumed									324	10	(11)
Ceded									14	18	(17)
Net									626	325	137
Premiums Earned:
Direct									509	693	887
Assumed									51	27	27
Ceded									(12)	(30)	(50)
Net earned premiums	$ 125	$ 142	$ 136	$ 145	$ 178	$ 186	$ 162	$ 164	548	690	864
Loss and LAE:
Direct									68	404	327
Assumed									(1)	11	0
Ceded									(3)	(27)	(32)
Net	$ 21	$ 17	$ 44	$ (18)	$ 34	$ 223	$ 72	$ 59	$ 64	$ 388	$ 295