Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 74.0	$ 65.1	$ 193.2	$ 187.2
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on securities, net of tax	(0.1)	0	0.1	(0.1)
Other comprehensive income (loss)	(0.1)	0	0.1	(0.1)
Comprehensive income	$ 73.9	$ 65.1	$ 193.3	$ 187.1