Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 69.4	$ 61.5	$ 119.2	$ 122.1
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on securities, net of tax	0.1	(0.2)	0.2	(0.1)
Other comprehensive income (loss)	0.1	(0.2)	0.2	(0.1)
Comprehensive income	$ 69.5	$ 61.3	$ 119.4	$ 122.0