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Fair Value (Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Beginning Balance | $ 26.1 | $ 27.3 | $ 27.1 | $ 28.0
Transfers out of Level 3 |  |  | (0.1) |
Included in net realized and unrealized investment gains (losses) | $ 0.1 |  | $ 0.2 | $ 0.1
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain Loss On Investments From Continuing Operations |  | Gain Loss On Investments From Continuing Operations | Gain Loss On Investments From Continuing Operations
Included in other comprehensive income (loss) - changes in net unrealized gains (losses) on investment securities | $ (0.1) | $ (0.3) | $ (0.2) | $ (0.2)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] | OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax | OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax | OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax | OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax
Settlements | $ (0.3) | $ (0.3) | $ (1.2) | $ (1.2)
Ending Balance | 25.8 | 26.7 | 25.8 | 26.7
Changes in net unrealized gains (losses) for the period included in other comprehensive income (loss) for assets held at the end of the period | $ (0.1) | $ (0.3) | $ (0.2) | $ (0.2)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Gain Loss On Investments From Continuing Operations | Gain Loss On Investments From Continuing Operations | Gain Loss On Investments From Continuing Operations | Gain Loss On Investments From Continuing Operations
Municipals [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Beginning Balance | $ 7.9 | $ 8.8 | $ 8.6 | $ 9.3
Included in other comprehensive income (loss) - changes in net unrealized gains (losses) on investment securities | 0.3 | (0.2) | 0.2 | (0.1)
Settlements | (0.2) | (0.1) | (0.8) | (0.7)
Ending Balance | 8.0 | 8.5 | 8.0 | 8.5
Changes in net unrealized gains (losses) for the period included in other comprehensive income (loss) for assets held at the end of the period | 0.3 | (0.2) | 0.2 | (0.1)
Corporates [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Beginning Balance |  | 0.1 | 0.1 | 0.1
Transfers out of Level 3 |  |  | (0.1) |
Ending Balance |  | 0.1 |  | 0.1
Commercial Mortgage-Backed [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Beginning Balance | 6.7 | 7.2 | 7.0 | 7.5
Included in other comprehensive income (loss) - changes in net unrealized gains (losses) on investment securities | (0.4) | (0.1) | (0.4) | (0.1)
Settlements | (0.1) | (0.2) | (0.4) | (0.5)
Ending Balance | 6.2 | 6.9 | 6.2 | 6.9
Changes in net unrealized gains (losses) for the period included in other comprehensive income (loss) for assets held at the end of the period | (0.4) | (0.1) | (0.4) | (0.1)
Debt Securities [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Beginning Balance | 14.6 | 16.1 | 15.7 | 16.9
Transfers out of Level 3 |  |  | (0.1) |
Included in other comprehensive income (loss) - changes in net unrealized gains (losses) on investment securities | (0.1) | (0.3) | (0.2) | (0.2)
Settlements | (0.3) | (0.3) | (1.2) | (1.2)
Ending Balance | 14.2 | 15.5 | 14.2 | 15.5
Changes in net unrealized gains (losses) for the period included in other comprehensive income (loss) for assets held at the end of the period | (0.1) | (0.3) | (0.2) | (0.2)
Equities Securities and Other [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Beginning Balance | 11.5 | 11.2 | 11.4 | 11.1
Included in net realized and unrealized investment gains (losses) | 0.1 |  | 0.2 | 0.1
Ending Balance | $ 11.6 | $ 11.2 | $ 11.6 | $ 11.2

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- Definition Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 101 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-101 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-3 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 102 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-102 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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- Definition Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3). + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 101 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-101 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-3 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 102 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-102 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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