Insurance Premiums and Service Revenue Earned Insurance Premiums and Service Revenue Earned (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance Premiums and Service Revenue [Line Items]
Insurance Services Revenue	$ 973	$ 945	$ 940
Insurance Premiums Written [Member]
Insurance Premiums and Service Revenue [Line Items]
Direct Premiums Written	384	317	313
Assumed Premiums Written	2	3	2
Proceeds from Insurance Premiums Collected	386	320	315
Ceded Premiums Written	(254)	(198)	(184)
Premiums Written, Net	132	122	131
Insurance Services Revenue	864	826	846
Insurance Premiums and Service Revenue	996	948	977
Insurance Premiums Earned [Member]
Insurance Premiums and Service Revenue [Line Items]
Direct Premiums Earned	364	318	296
Assumed Premiums Earned	5	5	16
Proceeds from Insurance Premiums Collected	369	323	312
Ceded Premiums Earned	(188)	(141)	(125)
Premiums Earned, Net	181	182	187
Insurance Services Revenue	792	763	753
Insurance Premiums and Service Revenue	$ 973	$ 945	$ 940