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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
LOANS AND LEASES
Balance at Beginning of Period	$ 147.2	$ 114.5	$ 104.5	$ 112.6
Charge-Offs	(0.4)	(0.6)	(2.2)	(1.6)
Recoveries	3.0	1.8	4.1	4.0
Net (Charge-Offs) Recoveries	2.6	1.2	1.9	2.4
Provision for Credit Losses	60.4	(4.9)	106.0	(4.2)
Balance at End of Period	210.2	110.8	210.2	110.8
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	40.4	24.9	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	8.6	(1.6)	20.2	(2.3)
Balance at End of Period	49.0	23.3	49.0	23.3
COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	94.7	58.1	58.1	57.6
Charge-Offs	0.0	0.0	(0.1)	(0.1)
Recoveries	1.3	0.3	2.0	0.7
Net (Charge-Offs) Recoveries	1.3	0.3	1.9	0.6
Provision for Credit Losses	66.8	1.5	108.7	1.7
Balance at End of Period	162.8	59.9	162.8	59.9
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	38.8	20.5	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	7.3	(2.0)	18.4	(2.6)
Balance at End of Period	46.1	18.5	46.1	18.5
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	52.5	56.4	46.4	55.0
Charge-Offs	(0.4)	(0.6)	(2.1)	(1.5)
Recoveries	1.7	1.5	2.1	3.3
Net (Charge-Offs) Recoveries	1.3	0.9	0.0	1.8
Provision for Credit Losses	(6.4)	(6.4)	(2.7)	(5.9)
Balance at End of Period	47.4	50.9	47.4	50.9
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	1.6	4.4	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	1.3	0.4	1.8	0.3
Balance at End of Period	$ 2.9	$ 4.8	2.9	$ 4.8
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