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Investments Distribution by External Credit Rating for Fixed Maturity Securities (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Debt Securities, Available-for-sale |  |
Fixed Maturity Securities | $ 33,190.2 | $ 35,629.9
Gross Unrealized Gain | 857.0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 2,513.3 |
Fixed maturity securities in unrealized loss position percent of total | 100.00% |
External Credit Rating, Investment Grade |  |
Debt Securities, Available-for-sale |  |
Fixed Maturity Securities | $ 31,942.8 |
Gross Unrealized Gain | 832.2 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 2,463.5 |
Fixed maturity securities in unrealized loss position percent of total | 98.00% |
External Credit Rating, Below-Investment-Grade |  |
Debt Securities, Available-for-sale |  |
Fixed Maturity Securities | $ 1,247.4 |
Gross Unrealized Gain | 24.8 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 49.8 |
Fixed maturity securities in unrealized loss position percent of total | 2.00% |

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