Consolidated Statements Of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other comprehensive income/(loss), tax	$ (11.5)	$ (20.2)	$ 11.2
Reclassifications to earnings of realized gains/(losses) on available-for-sale securities			(2.9)
Increase in accumulated comprehensive income		17.9
Reclassifications to earnings of gains/(losses) on cash flow hedging instruments		$ 3.3	$ 4.9
ASU 2019-04 [Member]
Increase in accumulated comprehensive income	17.9
ASU 2018-02 [Member]
Reclassification to retained earnings related to cash flow hedges and investment portfolio risk	$ 3.1