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Municipal Bond Guarantee Insurance - Schedule of change in the fair value of BAM surplus notes (Details) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2025 | Mar. 31, 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 |  |
Operating Segments | Financial Guarantee (HG Global) |  |  |  |
Changes In Nominal Value Of Surplus Notes [Roll Forward] |  |  |  |
Beginning nominal value | 495.7 |  |  |
Interest income from BAM Surplus Notes | 7.5 | $ 0.0 |  |
Payments of principal and interest | 0.0 |  |  |
Ending nominal value | 503.2 |  |  |
Changes In Fair Value Discount Of Surplus Notes [Roll Forward] |  |  |  |
Beginning fair value discount | (114.0) |  |  |
Change in fair value of BAM Surplus Notes | 0.0 |  |  |
Ending fair value discount | (114.0) |  |  |
BAM Surplus Notes, at fair value | $ 389.2 |  | $ 381.7 | $ 387.4

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