Consolidated Statements Of Comprehensive Income (Parenthetical) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Other comprehensive income/(loss), tax	$ 6.6	$ 26.1	$ 0.2	$ 1.4
Reclassifications to earnings of realized gains/(losses) on available-for-sale securities	$ 0.0		$ 0.0