Insurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statutory Accounting Practices [Line Items]
Cash and cash equivalents	$ 59	$ 162
Marketable securities	649	449
Total cash, cash equivalents, and marketable securities	708	611
Assets Held by Insurance Regulators	12	12
Prepaid reinsurance premiums and other reinsurance recoverables	658	611
Related party transaction, prepaid reinsurance premiums and other reinsurance recoverables	97	95
Earned insurance premiums	176	154	$ 133
Insurance loss and loss adjustment expenses	71	63	55
Unearned insurance premiums and fees	775	723
Related Party Transactions Unearned Premiums and Fees	667	621
Premiums Written and Earned [Abstract]
Direct premiums written	392	385	371
Assumed premiums written	0	0	0
Ceded premiums written	(225)	(227)	(215)
Net premiums written	167	158	156
Direct premiums earned	346	320	298
Assumed premiums earned	0	0	0
Ceded premiums earned	(179)	(162)	(142)
Premiums Earned, Net	167	158	156
Insurance Expenses [Abstract]
Insurance losses	101	143	146
Loss adjustment expenses	5	8	5
Reinsurance Income and Other Expenses, Net	(29)	(27)	(26)
Insurance expenses	77	124	125
Liability for reported insurance claims and estimate of unreported claims	11	8
Ceded insurance expenses	$ 114	$ 104	$ 95