Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 74.2	$ 69.4	$ 145.7	$ 119.2
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on securities, net of tax	(0.2)	0.1	0.1	0.2
Other comprehensive income (loss)	(0.2)	0.1	0.1	0.2
Comprehensive income	$ 74.0	$ 69.5	$ 145.8	$ 119.4