Allowance for Credit Losses (Changes in Allowance for Credit Losses Related to Loan and Leases) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
LOANS AND LEASES
Balance at Beginning of Period	$ 190.7	$ 104.5
Charge-Offs	(0.4)	(1.8)
Recoveries	1.3	1.1
Net (Charge-Offs) Recoveries	0.9	(0.7)
Provision for Credit Losses	(26.2)	45.6
Balance at End of Period	165.4	147.2
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	61.1	19.9
Charge-Offs	0.0	0.0
Recoveries	0.0	0.0
Net (Charge-Offs) Recoveries	0.0	0.0
Provision for Credit Losses	(6.0)	11.6
Balance at End of Period	55.1	40.4
COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	142.2	58.1
Charge-Offs	0.0	(0.1)
Recoveries	0.0	0.7
Net (Charge-Offs) Recoveries	0.0	0.6
Provision for Credit Losses	(17.5)	41.9
Balance at End of Period	124.7	94.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	57.6	15.8
Charge-Offs	0.0	0.0
Recoveries	0.0	0.0
Net (Charge-Offs) Recoveries	0.0	0.0
Provision for Credit Losses	(5.9)	11.1
Balance at End of Period	51.7	38.8
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	48.5	46.4
Charge-Offs	(0.4)	(1.7)
Recoveries	1.3	0.4
Net (Charge-Offs) Recoveries	0.9	(1.3)
Provision for Credit Losses	(8.7)	3.7
Balance at End of Period	40.7	52.5
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	3.5	4.1
Charge-Offs	0.0	0.0
Recoveries	0.0	0.0
Net (Charge-Offs) Recoveries	0.0	0.0
Provision for Credit Losses	(0.1)	0.5
Balance at End of Period	$ 3.4	1.6
Cumulative Effect Adjustment
LOANS AND LEASES
Balance at Beginning of Period		(2.2)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		8.9
Cumulative Effect Adjustment | COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period		(5.9)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		11.9
Cumulative Effect Adjustment | PERSONAL
LOANS AND LEASES
Balance at Beginning of Period		3.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		(3.0)
Adjusted Balance
LOANS AND LEASES
Balance at Beginning of Period		102.3
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		28.8
Adjusted Balance | COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period		52.2
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		27.7
Adjusted Balance | PERSONAL
LOANS AND LEASES
Balance at Beginning of Period		50.1
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		$ 1.1