v3.25.4
COMMITMENTS, CONTINGENCIES AND OTHER ITEMS - Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Commitments and Contingencies [Line Items]    
Unfunded commitments $ 3,900.0  
Operating lease, weighted average lease term 5 years 7 months 6 days  
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] Other assets Other assets
Operating Lease, Liability, Statement of Financial Position [Extensible List] Other liabilities Other liabilities
Operating lease, right-of-use asset $ 97.1 $ 83.8
Operating lease, liability 127.4 114.3
Operating lease, expense $ 15.6 $ 14.8
Lessee, finance lease, term of contract 20 years  
Lessee, finance lease, renewal term 30 years  
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] Other assets Other assets
Finance Lease, Liability, Statement of Financial Position [Extensible List] Other liabilities Other liabilities
Finance lease, right-of-use asset $ 15.6 $ 16.1
Finance lease, liability 20.4 21.0
Interest Expense    
Commitments and Contingencies [Line Items]    
Finance lease, interest expense 2.1 2.1
Other income (loss)    
Commitments and Contingencies [Line Items]    
Finance lease, right-of-use asset, amortization 0.5 $ 0.5
Letter of Credit    
Commitments and Contingencies [Line Items]    
Letters of credit outstanding 528.8  
Letter of Credit | Top Layer Reinsurance Ltd.    
Commitments and Contingencies [Line Items]    
Line of credit facility, maximum borrowing capacity 37.5  
Letter of Credit | Top Layer Reinsurance Ltd. | Capital Support Agreement    
Commitments and Contingencies [Line Items]    
Mandatory capital contribution in the event of capital and surplus reduction below a specified level $ 50.0