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Investment Income and Gains and Losses (Schedule of Net Realized and Unrealized Gains (Losses) on Investments Including Impairments) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Gain (Loss) on Investments [Line Items] |  |  |
Net realized and unrealized investment losses | $ (46.4) | $ (76.2) | $ (32.3)
Net realized and unrealized investment losses | (46.0) | (75.8) | (32.5)
Fixed Maturities [Member] |  |  |
Gain (Loss) on Investments [Line Items] |  |  |
Net realized and unrealized investment losses | (61.8) | (89.6) | (20.2)
Mortgage Loans on Real Estate [Member] |  |  |
Gain (Loss) on Investments [Line Items] |  |  |
Net realized and unrealized investment losses | (2.5) | (0.5) | (6.9)
Equity Securities [Member] |  |  |
Gain (Loss) on Investments [Line Items] |  |  |
Net realized and unrealized investment losses | 19.0 | 14.2 | (5.6)
Other Investments [Member] |  |  |
Gain (Loss) on Investments [Line Items] |  |  |
Net realized and unrealized investment losses | $ (0.7) | $ 0.1 | $ 0.2

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