Consolidated Statements Of Comprehensive Income (Parenthetical) (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Other comprehensive income/(loss), tax	$ (1.9)	$ 7.6	$ (2.0)	$ 6.4
Reclassifications to earnings of realized gains/(losses) on available-for-sale securities	$ 0.0		$ 0.0