Allowance for Credit Losses (Changes in Allowance for Credit Losses Related to Loan and Leases) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
LOANS AND LEASES
Balance at Beginning of Period	$ 104.5	$ 112.6	$ 131.2
Charge-Offs	(9.7)	(6.5)	(10.1)
Recoveries	6.5	7.2	9.0
Net Recoveries (Charge-Offs)	(3.2)	0.7	(1.1)
Provision for Credit Losses	91.6	(8.8)	(17.5)
Balance at End of Period	190.7	104.5	112.6
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	19.9	25.6	22.6
Charge-Offs	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0
Provision for Credit Losses	32.3	(5.7)	3.0
Balance at End of Period	61.1	19.9	25.6
Commercial
LOANS AND LEASES
Balance at Beginning of Period	58.1	57.6	63.5
Charge-Offs	(6.3)	(3.0)	(0.9)
Recoveries	2.4	0.9	1.7
Net Recoveries (Charge-Offs)	(3.9)	(2.1)	0.8
Provision for Credit Losses	93.9	2.6	(6.7)
Balance at End of Period	142.2	58.1	57.6
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	15.8	21.1	17.3
Charge-Offs	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0
Provision for Credit Losses	29.9	(5.3)	3.8
Balance at End of Period	57.6	15.8	21.1
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	46.4	55.0	67.7
Charge-Offs	(3.4)	(3.5)	(9.2)
Recoveries	4.1	6.3	7.3
Net Recoveries (Charge-Offs)	0.7	2.8	(1.9)
Provision for Credit Losses	(2.3)	(11.4)	(10.8)
Balance at End of Period	48.5	46.4	55.0
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	4.1	4.5	5.3
Charge-Offs	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0
Provision for Credit Losses	2.4	(0.4)	(0.8)
Balance at End of Period	3.5	4.1	$ 4.5
Cumulative Effect Adjustment
LOANS AND LEASES
Balance at Beginning of Period	(2.2)
Balance at End of Period		(2.2)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	8.9
Balance at End of Period		8.9
Cumulative Effect Adjustment | Commercial
LOANS AND LEASES
Balance at Beginning of Period	(5.9)
Balance at End of Period		(5.9)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	11.9
Balance at End of Period		11.9
Cumulative Effect Adjustment | PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	3.7
Balance at End of Period		3.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	(3.0)
Balance at End of Period		(3.0)
Adjusted Balance
LOANS AND LEASES
Balance at Beginning of Period	102.3
Balance at End of Period		102.3
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	28.8
Balance at End of Period		28.8
Adjusted Balance | Commercial
LOANS AND LEASES
Balance at Beginning of Period	52.2
Balance at End of Period		52.2
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	27.7
Balance at End of Period		27.7
Adjusted Balance | PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	50.1
Balance at End of Period		50.1
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	$ 1.1
Balance at End of Period		$ 1.1