Consolidated Statements Of Comprehensive Income (Parenthetical) (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other comprehensive income/(loss), tax	$ 7.6	$ 4.4	$ (6.4)	$ 18.1
Reclassifications to earnings of realized losses on available-for-sale securities			$ (0.3)	(0.2)
Transfer from held-to-maturity securities to available-for-sale, net of tax		17.9		17.9
Reclassifications to earnings of gains (loss) on cash flow hedging instruments		$ 0.6		2.9
ASU 2019-04 [Member]
Transfer from held-to-maturity securities to available-for-sale, net of tax				$ 17.9