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Investments - Net Investment Gains (Losses) by Transaction Type (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract] |  |
Credit loss impairments | $ 0.0 | $ (0.9)
Intent-to-sell impairments | 0.0 | 0.0
Total impairments | 0.0 | (0.9)
Sales and other, net | 0.2 | (0.1)
Change in fair value - equity securities | (1.2) | 2.6
Change in fair value and gains (losses) realized on settlements - derivatives | (2.3) | 0.6
Net investment gains (losses) | $ (3.3) | $ 2.2

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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://fasb.org/us-gaap/role/ref/legacyRef -Topic 815 -SubTopic 25 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480238/815-25-50-1 + Details
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- Definition Amount of writeoff of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-9 + Details
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