v3.26.1
Municipal Bond Guarantee Insurance - Narrative (Details)
$ in Millions
3 Months Ended
Mar. 31, 2026
USD ($)
Mar. 31, 2025
USD ($)
Dec. 31, 2025
USD ($)
Jul. 01, 2024
Jun. 30, 2024
Guarantor Obligations [Line Items]          
Member surplus contributions, insurance premium charges, percentage 55.00%        
Assets held-in-trust $ 1,008.9   $ 1,006.5    
Collateral trusts, investments and cash 319.4   323.3    
Surplus notes 276.8   276.8    
Interest receivable 6.9   7.0    
Debt 834.8   837.0    
Interest income from BAM Surplus Notes 6.9 $ 7.5      
HG Global          
Guarantor Obligations [Line Items]          
Assumed 8.3 6.7      
Premiums written, gross 8.3 6.7      
Gross earned premiums 7.7 8.2      
Operating Segments | Financial Guarantee (HG Global)          
Guarantor Obligations [Line Items]          
Debt 147.9   147.8    
Interest income from BAM Surplus Notes 6.9 7.5      
Notes receivable, fair value disclosure 345.9 389.2 339.0    
BAM Surplus Notes          
Guarantor Obligations [Line Items]          
Distribution received 15.0        
Accrued interest 7.1        
Cash distribution received $ 7.9        
BAM Surplus Notes | Surplus Notes          
Guarantor Obligations [Line Items]          
Basis spread on variable rate 3.00%        
Stated margin       10.00% 8.20%
Debt $ 276.8   276.8    
Interest receivable $ 220.6   $ 213.7    
BAM Surplus Notes | Surplus Notes | Discount Rate          
Guarantor Obligations [Line Items]          
Debt instrument, measurement input 0.0830   0.0805    
Subsidiary - HG Global          
Guarantor Obligations [Line Items]          
Purchase of surplus notes $ 503.0        
Percentage of risk premium ceded 60.00%        
Renegotiation period 5 years        
Premiums written, gross   6.7      
Gross earned premiums $ 7.7 $ 8.2      
Percent over a target trust balance 102.00%        
Subsidiary - HG Global | Regulation 114          
Guarantor Obligations [Line Items]          
Assets held-in-trust $ 405.8   $ 399.4    
Supplement trust target 603.0        
Subsidiary - HG Global | Supplemental Trust          
Guarantor Obligations [Line Items]          
Assets held-in-trust $ 603.1   $ 607.1    
Subsidiary - HG Global | Maximum          
Guarantor Obligations [Line Items]          
Percentage of par value of policy reinsured 15.00%        
Variable Interest Entity, Primary Beneficiary - Build America Mutual Assurance Company | Fidus Re Ltd.          
Guarantor Obligations [Line Items]          
Reinsured amount $ 125.0