Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 242.1	$ 165.4	$ 254.7	$ 494.2
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on securities, net of tax	(0.2)	0.1	0.9	1.2
Other comprehensive income (loss)	(0.2)	0.1	0.9	1.2
Comprehensive income	$ 241.9	$ 165.5	$ 255.6	$ 495.4