Allowance for Credit Losses (Changes in Allowance for Credit Losses Related to Loan and Leases) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
LOANS AND LEASES
Balance at Beginning of Period	$ 136.3	$ 165.4	$ 138.4	$ 190.7
Balance at End of Period	138.2	148.8	138.2	148.8
Charge-Offs	0.0	0.0	0.1	0.4
Recoveries	5.5	3.2	8.8	4.5
Net Recoveries (Charge-Offs)	5.5	3.2	8.7	4.1
Provision for Credit Losses	(3.6)	(19.8)	(8.9)	(46.0)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	37.5	55.1	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	6.0	(8.6)	9.4	(14.6)
Balance at End of Period	43.5	46.5	43.5	46.5
COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	102.5	124.7	105.6	142.2
Balance at End of Period	102.5	118.0	102.5	118.0
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.2	0.5	2.4	0.5
Net Recoveries (Charge-Offs)	0.2	0.5	2.4	0.5
Provision for Credit Losses	(0.2)	(7.2)	(5.5)	(24.7)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	34.7	51.7	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	5.6	(8.1)	8.9	(14.0)
Balance at End of Period	40.3	43.6	40.3	43.6
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	33.8	40.7	32.8	48.5
Balance at End of Period	35.7	30.8	35.7	30.8
Charge-Offs	0.0	0.0	0.1	0.4
Recoveries	5.3	2.7	6.4	4.0
Net Recoveries (Charge-Offs)	5.3	2.7	6.3	3.6
Provision for Credit Losses	(3.4)	(12.6)	(3.4)	(21.3)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	2.8	3.4	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	0.4	(0.5)	0.5	(0.6)
Balance at End of Period	$ 3.2	$ 2.9	$ 3.2	$ 2.9