Investment Income and Gains and Losses (Proceeds from Sales of Available for Sale Fixed Maturities) (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
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| Investments, Debt and Equity Securities [Abstract] | ||||
| Proceeds from sales | $ 256.5 | $ 358.4 | $ 1,044.5 | $ 1,260.4 |
| Gross gains | 0.2 | 0.4 | 3.0 | 1.7 |
| Gross losses | $ 8.6 | $ 21.6 | $ 23.9 | $ 46.8 |
| X | ||||||||||
- Definition Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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