Allowance for Credit Losses (Recorded Investments in Loans and Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Loans and Leases
Evaluated on an Individual Basis	$ 109.1	$ 166.6
Evaluated on a Collective Basis	42,784.2	40,314.0
TOTAL LOANS AND LEASES	42,893.3	40,480.6
Allowance for Credit Losses on Loans and Leases
Evaluated on an Individual Basis	10.4	10.1
Evaluated on a Collective Basis	133.9	128.3
Allowance Assigned to Loans and Leases	144.3	138.4	$ 190.7	$ 104.5
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0	0.0
Evaluated on a Collective Basis	38.5	34.1
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	38.5	34.1	61.1	19.9
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	182.8	172.5
Commercial
Loans and Leases
Evaluated on an Individual Basis	63.0	92.1
Evaluated on a Collective Basis	21,572.6	18,395.3
TOTAL LOANS AND LEASES	21,635.6	18,487.4
Allowance for Credit Losses on Loans and Leases
Evaluated on an Individual Basis	10.4	10.1
Evaluated on a Collective Basis	105.8	95.5
Allowance Assigned to Loans and Leases	116.2	105.6	142.2	58.1
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0	0.0
Evaluated on a Collective Basis	36.3	31.4
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	36.3	31.4	57.6	15.8
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	152.5	137.0
PERSONAL
Loans and Leases
Evaluated on an Individual Basis	46.1	74.5
Evaluated on a Collective Basis	21,211.6	21,918.7
TOTAL LOANS AND LEASES	21,257.7	21,993.2
Allowance for Credit Losses on Loans and Leases
Evaluated on an Individual Basis	0.0	0.0
Evaluated on a Collective Basis	28.1	32.8
Allowance Assigned to Loans and Leases	28.1	32.8	48.5	46.4
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0.0	0.0
Evaluated on a Collective Basis	2.2	2.7
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	2.2	2.7	$ 3.5	$ 4.1
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	$ 30.3	$ 35.5