Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
LOANS AND LEASES
Balance at Beginning of Period	$ 138.4	$ 190.7
Charge-Offs	(0.1)	(0.4)
Recoveries	3.3	1.3
Net Recoveries (Charge-Offs)	3.2	0.9
Provision for Credit Losses	(5.3)	(26.2)
Balance at End of Period	136.3	165.4
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	34.1	61.1
Charge-Offs	0.0	0.0
Recoveries	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0
Provision for Credit Losses	3.4	(6.0)
Balance at End of Period	37.5	55.1
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	11.2	7.3
Charge-Offs	0.0	0.0
Recoveries	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0
Provision for Credit Losses	3.4	1.3
Balance at End of Period	14.6	8.6
OTHER FINANCIAL ASSETS
Balance at Beginning of Period	1.0	0.8
Charge-Offs	0.0	0.0
Recoveries	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0
Provision for Credit Losses	0.1	0.9
Balance at End of Period	1.1	1.7
TOTAL
Balance at Beginning of Period	184.7	259.9
Charge-Offs	(0.1)	(0.4)
Recoveries	3.3	1.3
Net Recoveries (Charge-Offs)	3.2	0.9
Provision for Credit Losses	1.6	(30.0)
Balance at End of Period	$ 189.5	$ 230.8