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Investments Distribution by External Credit Rating for Fixed Maturity Securities (Details) - USD ($) $ in Millions | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Debt Securities, Available-for-sale |  |
Fixed Maturity Securities | $ 35,952.8 | $ 36,833.9
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 723.4 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 3,319.8 |
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 | $ 34,515.0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 709.6 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 3,227.0 |
Fixed maturity securities in unrealized loss position percent of total | 97.20% |
External Credit Rating, Below-Investment-Grade |  |
Debt Securities, Available-for-sale |  |
Fixed Maturity Securities | $ 1,437.8 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 13.8 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 92.8 |
Fixed maturity securities in unrealized loss position percent of total | 2.80% |

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