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Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Schedule of (Favorable) Unfavorable Loss and LAE Reserve Development) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items] |  |  |
Loss and LAE reserve development, including catastrophes | $ (96.4) | $ (109.4) | $ (15.9)
Core Commercial [Member] |  |  |
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items] |  |  |
Loss and LAE reserve development, including catastrophes | (18.1) | (50.0) | (2.0)
Specialty [Member] |  |  |
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items] |  |  |
Loss and LAE reserve development, including catastrophes | (60.8) | (60.9) | (57.1)
Personal Lines [Member] |  |  |
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items] |  |  |
Loss and LAE reserve development, including catastrophes | (18.2) | 0.1 | 40.9
Other [Member] |  |  |
Shortduration Insurance Contracts Reconciliation Of Claims Development To Liability [Line Items] |  |  |
Loss and LAE reserve development, including catastrophes | $ 0.7 | $ 1.4 | $ 2.3

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