Allowance for Credit Losses (Recorded Investments in Loans and Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases
Evaluated on an Individual Basis	$ 166.6	$ 131.7
Evaluated on a Collective Basis	40,314.0	33,628.0
TOTAL LOANS AND LEASES	40,480.6	33,759.7
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	10.1	9.1
Evaluated on a Collective Basis	128.3	181.6
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	138.4	190.7	$ 104.5	$ 112.6
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0	1.6
Evaluated on a Collective Basis	34.1	59.5
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	34.1	61.1	19.9	25.6
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	172.5	251.8
COMMERCIAL
Loans and Leases
Evaluated on an Individual Basis	92.1	66.6
Evaluated on a Collective Basis	18,395.3	15,195.4
TOTAL LOANS AND LEASES	18,487.4	15,262.0
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	10.1	8.8
Evaluated on a Collective Basis	95.5	133.4
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	105.6	142.2	58.1	57.6
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0	1.6
Evaluated on a Collective Basis	31.4	56.0
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	31.4	57.6	15.8	21.1
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	137.0	199.8
PERSONAL
Loans and Leases
Evaluated on an Individual Basis	74.5	65.1
Evaluated on a Collective Basis	21,918.7	18,432.6
TOTAL LOANS AND LEASES	21,993.2	18,497.7
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	0.0	0.3
Evaluated on a Collective Basis	32.8	48.2
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	32.8	48.5	46.4	55.0
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0	0.0
Evaluated on a Collective Basis	2.7	3.5
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	2.7	3.5	$ 4.1	$ 4.5
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	$ 35.5	$ 52.0