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Investments - Change in Allowance for Credit Losses on Fixed Maturities Available-for-Sale (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward] |  |
Balance, Beginning of Year | $ 8.2 | $ 9.6
Additions for Securities for which No Previous Expected Credit Losses were Recognized | 3.4 | 2.9
Reductions due to Sales | (0.8) | (2.6)
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized | (0.1) | (0.9)
Write-offs Charged Against Allowance |  | (0.8)
Balance, End of Year | 10.7 | 8.2
States and Political Subdivisions |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward] |  |
Balance, Beginning of Year | 0.5 | 0.7
Additions for Securities for which No Previous Expected Credit Losses were Recognized | 0.0 | 0.0
Reductions due to Sales | 0.0 | 0.0
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized | 0.2 | (0.2)
Write-offs Charged Against Allowance |  | (0.4)
Balance, End of Year | 0.3 | 0.5
Bonds and Notes |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward] |  |
Balance, Beginning of Year | 7.7 | 8.9
Additions for Securities for which No Previous Expected Credit Losses were Recognized | 3.4 | 2.9
Reductions due to Sales | (0.8) | (2.6)
Net (Decrease) Increase in Allowance on Securities for which Expected Credit Losses were Previously Recognized | 0.1 | (1.1)
Write-offs Charged Against Allowance |  | (0.4)
Balance, End of Year | $ 10.4 | $ 7.7

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- Definition Debt Securities, Available-for-Sale, Allowance for Credit Loss Including Variable Interest Entity + References No definition available. + Details
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- Definition Amount of expense 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), for which no credit loss was previously recorded. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-9 + Details
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- Definition Amount of expense (reversal of expense) for 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), not intended to be sold and not more likely than not will be required to sell before recovery of amortized cost basis, with previously recorded allowance. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-9 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of decrease in 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) from sale. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-9 + 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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