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Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive loss) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Net realized losses from sales and other | $ (61.7) | $ (84.2) | $ (8.9)
Income from continuing operations before income taxes | 843.8 | 537.8 | 41.1
Loss adjustment expenses and other operating expenses | (3,729.3) | (3,757.4) | (4,134.6)
Income tax (expense) benefit | (183.1) | (112.5) | (7.6)
Income from continuing operations | (660.7) | (425.3) | (33.5)
Net income | 662.5 | 426.0 | 35.3
Life [Member] |  |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Income from discontinued life businesses | 1.5 | 0.0 | 0.6
Reclassification out of Accumulated Other Comprehensive Loss [Member] |  |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Net income | (52.7) | (74.8) | (19.5)
Net Unrealized Appreciation (Depreciation) on Investments [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member] |  |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Net realized losses from sales and other | (61.6) | (88.0) | (9.1)
Impairments on investments | (0.2) | (1.7) | (11.1)
Income from continuing operations before income taxes | (61.8) | (89.7) | (20.2)
Income tax (expense) benefit | 13.7 | 20.1 | 5.6
Net income | (48.5) | (69.9) | (14.6)
Net Unrealized Appreciation (Depreciation) on Investments [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member] | Accelerated Share Repurchase Agreement [Member] |  |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Income from continuing operations | (48.1) | (69.6) | (14.6)
Net Unrealized Appreciation (Depreciation) on Investments [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member] | Life [Member] |  |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Income from discontinued life businesses | (0.4) | (0.3) | 0.0
Defined Benefit Pension and Postretirement Plans [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member] |  |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Loss adjustment expenses and other operating expenses | (6.7) | (6.8) | (7.9)
Income tax (expense) benefit | 1.4 | 1.4 | 1.7
Income from continuing operations | (5.3) | (5.4) | (6.2)
Net change in market risk | Reclassification out of Accumulated Other Comprehensive Loss [Member] |  |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Income tax (expense) benefit | (0.3) | (0.1) | (0.3)
Income from discontinued life businesses | 1.1 | 0.5 | 1.3
Net change in market risk | Reclassification out of Accumulated Other Comprehensive Loss [Member] | Life [Member] |  |  |
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] |  |  |
Income from discontinued life businesses | $ 1.4 | $ 0.6 | $ 1.6

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