Municipal Bond Guarantee Reinsurance - Schedule of Change in the Fair Value of BAM Surplus Notes (Details) - USD ($) |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
Dec. 31, 2025 |
|
| Changes In Nominal Value Of Surplus Notes [Roll Forward] | |||||
| Interest income from BAM Surplus Notes | $ 6,800,000 | $ 7,500,000 | $ 20,600,000 | $ 22,500,000 | |
| Changes In Fair Value Discount Of Surplus Notes [Roll Forward] | |||||
| Change in fair value of BAM Surplus Notes | (16,100,000) | (16,100,000) | 0 | ||
| Operating Segments | HG Global | |||||
| Changes In Nominal Value Of Surplus Notes [Roll Forward] | |||||
| Beginning nominal value | 504,300,000 | 510,700,000 | 490,500,000 | 495,700,000 | |
| Interest income from BAM Surplus Notes | 6,800,000 | 7,500,000 | 20,600,000 | 22,500,000 | |
| Payments of principal and interest | 8,000,000.0 | 8,000,000.0 | 8,000,000.0 | 8,000,000.0 | |
| Ending nominal value | 503,100,000 | 510,200,000 | 503,100,000 | 510,200,000 | |
| Changes In Fair Value Discount Of Surplus Notes [Roll Forward] | |||||
| Beginning fair value discount | (151,500,000) | (114,000,000.0) | (151,500,000) | (114,000,000.0) | |
| Change in fair value of BAM Surplus Notes | (16,100,000) | 0 | (16,100,000) | 0 | |
| Ending fair value discount | (167,600,000) | (114,000,000.0) | (167,600,000) | (114,000,000.0) | |
| BAM Surplus Notes, at fair value | $ 335,500,000 | $ 396,200,000 | $ 335,500,000 | $ 396,200,000 | $ 339,000,000.0 |