Municipal Bond Guarantee Insurance - Schedule of Change in the Fair Value of BAM Surplus Notes (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||||
|---|---|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
Dec. 31, 2024 |
Jul. 01, 2024 |
|
| Changes In Nominal Value Of Surplus Notes [Roll Forward] | ||||||
| Interest income from BAM Surplus Notes | $ 7.5 | $ 0.0 | $ 15.0 | $ 0.0 | ||
| Operating Segments | Financial Guarantee (HG Global) | ||||||
| Changes In Nominal Value Of Surplus Notes [Roll Forward] | ||||||
| Beginning nominal value | 503.2 | 495.7 | ||||
| Interest income from BAM Surplus Notes | 7.5 | $ 0.0 | 15.0 | $ 0.0 | ||
| Payments of principal and interest | 0.0 | 0.0 | ||||
| Ending nominal value | 510.7 | 510.7 | ||||
| Changes In Fair Value Discount Of Surplus Notes [Roll Forward] | ||||||
| Beginning fair value discount | (114.0) | (114.0) | ||||
| Change in fair value of BAM Surplus Notes | 0.0 | 0.0 | ||||
| Ending fair value discount | (114.0) | (114.0) | ||||
| BAM Surplus Notes, at fair value | $ 396.7 | $ 396.7 | $ 381.7 | $ 387.4 | ||