Reinsurance - Effect of Reinsurance on Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Premiums Written:
Direct									$ 663	$ 288	$ 297
Assumed									14	324	10
Ceded									10	14	18
Net									687	626	325
Premiums Earned:
Direct									429	509	693
Assumed									54	51	27
Ceded									(7)	(12)	(30)
Net earned premiums	$ 123	$ 123	$ 112	$ 118	$ 125	$ 142	$ 136	$ 145	476	548	690
Loss and LAE:
Direct									101	68	404
Assumed									2	(1)	11
Ceded									(10)	(3)	(27)
Net	$ 18	$ 30	$ (1)	$ 46	$ 21	$ 17	$ 44	$ (18)	$ 93	$ 64	$ 388