Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 250.0	$ 242.1	$ 740.7	$ 254.7
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on securities, net of tax	(0.2)	(0.2)	(0.9)	0.9
Other comprehensive gain (loss)	(0.2)	(0.2)	(0.9)	0.9
Comprehensive income	$ 249.8	$ 241.9	$ 739.8	$ 255.6