v3.25.2
Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Dec. 31, 2024
LOANS          
Balance at Beginning of Period $ 167.1 $ 162.4 $ 168.0 $ 178.7 $ 178.7
Charge-Offs (0.1) (0.3) (0.4) (11.4) (15.5)
Recoveries 0.4 0.4 0.9 1.1  
Net Recoveries (Charge-Offs) 0.3 0.1 0.5 (10.3)  
Provision for Credit Losses 13.1 5.2 12.0 (0.7)  
Balance at End of Period 180.5 167.7 180.5 167.7 168.0
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT          
Balance at Beginning of Period 32.8 25.2 30.4 26.9 26.9
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 1.9 4.3 4.3 2.6  
Balance at End of Period 34.7 29.5 34.7 29.5 30.4
HELD TO MATURITY DEBT SECURITIES          
Balance at Beginning of Period 6.7 12.4 6.5 12.7 12.7
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 0.2 (1.5) 0.4 (1.8)  
Balance at End of Period 6.9 10.9 6.9 10.9 6.5
OTHER FINANCIAL ASSETS          
Balance at Beginning of Period 0.7 1.0 1.0 0.9 0.9
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 0.4 (0.1) 0.1 0.0  
Balance at End of Period 1.1 0.9 1.1 0.9 1.0
TOTAL          
Balance at Beginning of Period 207.3 201.0 205.9 219.2 219.2
Charge-Offs (0.1) (0.3) (0.4) (11.4)  
Recoveries 0.4 0.4 0.9 1.1  
Net Recoveries (Charge-Offs) 0.3 0.1 0.5 (10.3)  
Provision for credit losses 15.6 7.9 16.8 0.1  
Balance at End of Period 223.2 209.0 223.2 209.0 205.9
Corporate Debt          
HELD TO MATURITY DEBT SECURITIES          
Balance at Beginning of Period 0.3 0.8 0.3 0.9 0.9
Provision for Credit Losses 0.0 (0.3) 0.0 (0.4)  
Balance at End of Period 0.3 0.5 0.3 0.5 $ 0.3
TOTAL          
Provision for credit losses $ 0.9 $ 0.1 $ 0.7 $ (0.6)