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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
LOANS AND LEASES
Balance at Beginning of Period	$ 210.2	$ 110.8	$ 104.5	$ 112.6
Charge-Offs	(0.8)	(1.1)	(3.0)	(2.7)
Recoveries	1.2	1.7	5.3	5.7
Net (Charge-Offs) Recoveries	0.4	0.6	2.3	3.0
Provision for Credit Losses	4.8	(5.7)	110.8	(9.9)
Balance at End of Period	215.4	105.7	215.4	105.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	49.0	23.3	19.9	25.6
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net (Charge-Offs) Recoveries	0.0	0.0	0.0	0.0
Provision for Credit Losses	(4.1)	(1.3)	16.1	(3.6)
Balance at End of Period	44.9	22.0	44.9	22.0
COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	162.8	59.9	58.1	57.6
Charge-Offs	0.0	0.0	(0.1)	(0.1)
Recoveries	0.2	0.0	2.2	0.7
Net (Charge-Offs) Recoveries	0.2	0.0	2.1	0.6
Provision for Credit Losses	(15.4)	(1.3)	93.3	0.4
Balance at End of Period	147.6	58.6	147.6	58.6
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	46.1	18.5	15.8	21.1
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net (Charge-Offs) Recoveries	0.0	0.0	0.0	0.0
Provision for Credit Losses	(6.0)	(0.7)	12.4	(3.3)
Balance at End of Period	40.1	17.8	40.1	17.8
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	47.4	50.9	46.4	55.0
Charge-Offs	(0.8)	(1.1)	(2.9)	(2.6)
Recoveries	1.0	1.7	3.1	5.0
Net (Charge-Offs) Recoveries	0.2	0.6	0.2	2.4
Provision for Credit Losses	20.2	(4.4)	17.5	(10.3)
Balance at End of Period	67.8	47.1	67.8	47.1
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	2.9	4.8	4.1	4.5
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net (Charge-Offs) Recoveries	0.0	0.0	0.0	0.0
Provision for Credit Losses	1.9	(0.6)	3.7	(0.3)
Balance at End of Period	$ 4.8	$ 4.2	4.8	$ 4.2
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