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Investments Distribution by External Credit Rating for Fixed Maturity Securities (Details) - USD ($) $ in Millions | Jun. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Debt Securities, Available-for-sale |  |
Fixed Maturity Securities | $ 35,374.1 | $ 34,840.8
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 810.6 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 3,464.6 |
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 | $ 33,559.1 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 801.4 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 3,314.9 |
Fixed maturity securities in unrealized loss position percent of total | 95.70% |
External Credit Rating, Below-Investment-Grade |  |
Debt Securities, Available-for-sale |  |
Fixed Maturity Securities | $ 1,815.0 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 9.2 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 149.7 |
Fixed maturity securities in unrealized loss position percent of total | 4.30% |

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