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v3.25.4

Investments (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2025 | Dec. 31, 2024
Schedule of Investments [Line Items] |  |
Other investments | $ 661.4 | $ 709.9
Concentration of investment in a single investee, maximum | 10.00% | 10.00%
Contractual investment commitments | $ 283.7 |
U.S. Government |  |
Schedule of Investments [Line Items] |  |
Marketable securities, fixed maturities |  | $ 304.9
Mortgage Loan Participations [Member] |  |
Schedule of Investments [Line Items] |  |
Due in current fiscal year, amortized cost | 59.6 |
Due in year one, amortized cost | 29.4 |
Due in year two, amortized cost | 20.8 |
Due in year three, amortized cost | 46.4 |
Due in year four and thereafter, amortized cost | 90.8 |
U.S. Treasury and Government Agencies [Member] |  |
Schedule of Investments [Line Items] |  |
Securities on loan, fair value | 356.4 | 316.3
Mortgage Loans on Real Estate [Member] |  |
Schedule of Investments [Line Items] |  |
Other investments | 247.0 | 304.9
Limited Partnership [Member] |  |
Schedule of Investments [Line Items] |  |
Other investments | 391.5 | 395.0
Federal Home Loan Bank of Boston [Member] |  |
Schedule of Investments [Line Items] |  |
Securities on loan, fair value | $ 339.2 | $ 130.9

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