Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 288.6	$ 96.4	$ 490.7	$ 12.6
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on securities, net of tax	0.0	1.2	(0.7)	1.1
Other comprehensive gain (loss)	0.0	1.2	(0.7)	1.1
Comprehensive income	$ 288.6	$ 97.6	$ 490.0	$ 13.7