Consolidated Statements Of Comprehensive Income (Parenthetical) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Other comprehensive income/(loss), tax	$ 26.1	$ 3.9	$ (1.4)	$ 13.7
Reclassifications to earnings of realized losses on available-for-sale securities	0.2	(0.2)	$ (0.3)	(0.2)
Reclassifications to earnings of gains (loss) on cash flow hedging instruments	$ (0.2)	$ 0.8		$ 2.3