Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 74.4	$ 71.5
Other comprehensive income, net of tax:
Unrealized gain (loss) on securities, net of tax	0.4	0.3
Other comprehensive income	0.4	0.3
Comprehensive income	$ 74.8	$ 71.8