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Investments - Net Investment Gains (Losses) by Transaction Type (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Investments, Debt and Equity Securities [Abstract] |  |  |  |
Credit loss impairments | $ 1.0 | $ (0.5) | $ (1.2) | $ (0.5)
Intent-to-sell impairments | (0.7) | (0.2) | (1.6) | (0.2)
Total impairments | 0.3 | (0.7) | (2.8) | (0.7)
Sales and other, net | 0.3 | 0.1 | 4.4 | (3.2)
Change in fair value - equity securities | 2.2 | 5.2 | 0.3 | 5.7
Change in fair value and gains (losses) realized on settlements - derivatives | 0.5 | (0.8) | (7.8) | (1.7)
Net investment gains (losses) | $ 3.3 | $ 3.8 | $ (5.9) | $ 0.1

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- Definition Other Than Temporary Impairment Losses, Investments, Portion Recognized In Earnings, Change In Intent + References No definition available. + Details
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- Definition Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 220 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 21 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147476148/220-40-50-21 + Details
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