Allowance for Credit Losses (Recorded Investments in Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Loans
Evaluated on an Individual Basis	$ 100.9	$ 65.9
Evaluated on a Collective Basis	41,847.4	43,324.7
TOTAL LOANS	41,948.3	43,390.6
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	10.2	3.2
Evaluated on a Collective Basis	154.1	164.8
Allowance Assigned to Loans	164.3	168.0	$ 178.7	$ 144.3
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit - Evaluated on a Collective Basis	23.3	30.4	26.9	38.5
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	187.6	198.4
Commercial
Loans
Evaluated on an Individual Basis	55.0	35.9
Evaluated on a Collective Basis	20,376.0	20,242.9
TOTAL LOANS	20,431.0	20,278.8
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	5.9	1.2
Evaluated on a Collective Basis	126.6	137.3
Allowance Assigned to Loans	132.5	138.5	146.8	116.2
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit - Evaluated on a Collective Basis	21.7	28.3	24.9	36.3
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	154.2	166.8
Personal
Loans
Evaluated on an Individual Basis	45.9	30.0
Evaluated on a Collective Basis	21,471.4	23,081.8
TOTAL LOANS	21,517.3	23,111.8
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	4.3	2.0
Evaluated on a Collective Basis	27.5	27.5
Allowance Assigned to Loans	31.8	29.5	31.9	28.1
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit - Evaluated on a Collective Basis	1.6	2.1	$ 2.0	$ 2.2
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	$ 33.4	$ 31.6