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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
LOANS AND LEASES
Balance at Beginning of Period	$ 165.4	$ 147.2	$ 190.7	$ 104.5
Charge-Offs	0.0	(0.4)	(0.4)	(2.2)
Recoveries	3.2	3.0	4.5	4.1
Net Recoveries (Charge-Offs)	3.2	2.6	4.1	1.9
Provision for Credit Losses	(19.8)	60.4	(46.0)	106.0
Balance at End of Period	148.8	210.2	148.8	210.2
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	55.1	40.4	61.1	19.9
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0	0.0
Provision for Credit Losses	(8.6)	8.6	(14.6)	20.2
Balance at End of Period	46.5	49.0	46.5	49.0
COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	124.7		142.2	58.1
Charge-Offs	0.0	0.0	0.0	(0.1)
Recoveries	0.5	1.3	0.5	2.0
Net Recoveries (Charge-Offs)	0.5	1.3	0.5	1.9
Provision for Credit Losses	(7.2)	66.8	(24.7)	108.7
Balance at End of Period	118.0	162.8	118.0	162.8
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	51.7		57.6	15.8
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0	0.0
Provision for Credit Losses	(8.1)	7.3	(14.0)	18.4
Balance at End of Period	43.6	46.1	43.6	46.1
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	40.7		48.5	46.4
Charge-Offs	0.0	(0.4)	(0.4)	(2.1)
Recoveries	2.7	1.7	4.0	2.1
Net Recoveries (Charge-Offs)	2.7	1.3	3.6	0.0
Provision for Credit Losses	(12.6)	(6.4)	(21.3)	(2.7)
Balance at End of Period	30.8	47.4	30.8	47.4
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	3.4		3.5	4.1
Charge-Offs	0.0	0.0	0.0	0.0
Recoveries	0.0	0.0	0.0	0.0
Net Recoveries (Charge-Offs)	0.0	0.0	0.0	0.0
Provision for Credit Losses	(0.5)	1.3	(0.6)	1.8
Balance at End of Period	$ 2.9	2.9	2.9	2.9
Cumulative Effect, Period of Adoption, 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, Period of Adoption, 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, Period of Adoption, 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		147.2	190.7	102.3
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		40.4	61.1	28.8
Adjusted Balance | COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period		94.7	142.2	52.2
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		38.8	57.6	27.7
Adjusted Balance | PERSONAL
LOANS AND LEASES
Balance at Beginning of Period		52.5	48.5	50.1
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		$ 1.6	$ 3.5	$ 1.1