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Municipal Bond Guarantee Insurance - Schedule of Change in the Fair Value of BAM Surplus Notes (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | Jul. 01, 2024
Changes In Nominal Value Of Surplus Notes [Roll Forward] |  |  |  |
Interest income from BAM Surplus Notes | $ 29.8 | $ 15.8 | $ 0.0 |
Changes In Fair Value Discount Of Surplus Notes [Roll Forward] |  |  |  |
Change in fair value of BAM Surplus Notes | (37.5) | 0.5 | 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 | 29.8 | 15.8 | 0.0 |
Payments of principal and interest | (35.0) |  |  |
Ending nominal value | 490.5 | 495.7 |  |
Changes In Fair Value Discount Of Surplus Notes [Roll Forward] |  |  |  |
Beginning fair value discount | (114.0) |  |  |
Change in fair value of BAM Surplus Notes | (37.5) | 0.5 | $ 0.0 |
Ending fair value discount | (151.5) | (114.0) |  |
Notes receivable, fair value disclosure | $ 339.0 | $ 381.7 |  | $ 387.4

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