Allowance for Credit Losses (Changes in Allowance for Credit Losses Related to Loan and Leases) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
LOANS AND LEASES
Balance at Beginning of Period	$ 138.2	$ 148.8	$ 138.4	$ 190.7
Balance at End of Period	138.7	143.9	138.7	143.9
Charge-Offs	5.4	0.0	5.5	0.4
Recoveries	0.9	1.1	9.7	5.6
Net Recoveries (Charge-Offs)	(4.5)	1.1	4.2	5.2
Provision for Credit Losses	5.0	(6.0)	(3.9)	(52.0)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	43.5	46.5	34.1	61.1
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0	0.0
Provision for Credit Losses	(2.8)	(6.7)	6.6	(21.3)
Balance at End of Period	40.7	39.8	40.7	39.8
COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	102.5	118.0	105.6	142.2
Balance at End of Period	100.6	115.7	100.6	115.7
Charge-Offs	4.9	0.0	4.9	0.0
Recoveries	0.3	0.4	2.7	0.9
Net Recoveries (Charge-Offs)	(4.6)	0.4	(2.2)	0.9
Provision for Credit Losses	2.7	(2.7)	(2.8)	(27.4)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	40.3	43.6	31.4	57.6
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0	0.0
Provision for Credit Losses	(2.8)	(6.4)	6.1	(20.4)
Balance at End of Period	37.5	37.2	37.5	37.2
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	35.7	30.8	32.8	48.5
Balance at End of Period	38.1	28.2	38.1	28.2
Charge-Offs	0.5	0.0	0.6	0.4
Recoveries	0.6	0.7	7.0	4.7
Net Recoveries (Charge-Offs)	0.1	0.7	6.4	4.3
Provision for Credit Losses	2.3	(3.3)	(1.1)	(24.6)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	3.2	2.9	2.7	3.5
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0	0.0
Provision for Credit Losses	0.0	(0.3)	0.5	(0.9)
Balance at End of Period	$ 3.2	$ 2.6	$ 3.2	$ 2.6