Allowance for Credit Losses (Changes in Allowance for Credit Losses Related to Loan and Leases) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
LOANS AND LEASES
Balance at Beginning of Period	$ 104.5
Charge-Offs	(1.8)	$ (1.0)
Recoveries	1.1	2.2
Net (Charge-Offs) Recoveries	(0.7)	1.2
Provision for Credit Losses	45.6	0.7
Balance at End of Period	40.4	24.9
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	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	11.6	(0.7)
Balance at End of Period	147.2	114.5
COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	58.1
Charge-Offs	(0.1)	(0.1)
Recoveries	0.7	0.4
Net (Charge-Offs) Recoveries	0.6	0.3
Provision for Credit Losses	41.9	0.2
Balance at End of Period	38.8	20.5
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	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	11.1	(0.6)
Balance at End of Period	94.7	58.1
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	46.4
Charge-Offs	(1.7)	(0.9)
Recoveries	0.4	1.8
Net (Charge-Offs) Recoveries	(1.3)	0.9
Provision for Credit Losses	3.7	0.5
Balance at End of Period	1.6	4.4
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	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	0.5	(0.1)
Balance at End of Period	52.5	56.4
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	112.6
Balance at End of Period		24.9
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	28.8	25.6
Balance at End of Period		114.5
Adjusted Balance | COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	52.2	57.6
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	27.7	21.1
Adjusted Balance | PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	50.1	55.0
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	$ 1.1	$ 4.5