CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Professional service revenues	$ 458	$ 447	$ 401
Insurance service revenues	2,817	2,613	2,258
Total revenues	3,275	3,060	2,659
Insurance costs	2,466	2,414	2,112
Cost of providing services (exclusive of depreciation and amortization of intangible assets)	213	190	151
Sales and marketing	187	174	167
General and administrative	114	92	69
Systems development and programming	45	31	28
Depreciation	28	19	15
Amortization of intangible assets	5	16	39
Total costs and operating expenses	3,058	2,936	2,581
Operating income	217	124	78
Other income (expense):
Interest expense and bank fees	(20)	(20)	(19)
Other, net	3	0	1
Income before provision for income taxes	200	104	60
Income tax expense	22	43	28
Net income	178	61	32
Other comprehensive income (loss), net of tax	0	1	(1)
Comprehensive income	$ 178	$ 62	$ 31
Net income per share:
Basic (in dollars per share)	$ 2.57	$ 0.88	$ 0.45
Diluted (in dollars per share)	$ 2.49	$ 0.85	$ 0.44
Weighted average shares:
Basic (in shares)	69,175,377	70,159,696	70,228,159
Diluted (in shares)	71,385,280	71,972,486	72,618,069