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v3.25.2

Investments - Summary of Fair Value and Amortized Costs (Details) - USD ($) $ in Millions | Jun. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Schedule of Investments [Line Items] |  |
Amortized Cost, net | $ 5,847.4 | $ 5,842.5
Fair Value | 5,453.3 | 5,387.9
Fixed maturity securities |  |
Schedule of Investments [Line Items] |  |
Amortized Cost, net | 5,847.4 | 5,842.5
Gross Unrealized Gains | 60.4 | 48.4
Gross Unrealized Losses | 454.5 | 503.0
Fair Value | 5,453.3 | 5,387.9
Mortgage-backed securities |  |
Schedule of Investments [Line Items] |  |
Amortized Cost, net | 643.5 | 827.9
Gross Unrealized Gains | 5.5 | 2.7
Gross Unrealized Losses | 43.5 | 74.8
Fair Value | 605.5 | 755.8
Other, including U.S. Treasury securities |  |
Schedule of Investments [Line Items] |  |
Amortized Cost, net | 424.4 | 426.5
Gross Unrealized Gains | 0.7 | 0.1
Gross Unrealized Losses | 61.5 | 69.0
Fair Value | 363.6 | 357.6
Municipal bonds |  |
Schedule of Investments [Line Items] |  |
Amortized Cost, net | 1,240.0 | 1,239.1
Gross Unrealized Gains | 17.5 | 17.5
Gross Unrealized Losses | 105.6 | 105.8
Fair Value | 1,151.9 | 1,150.8
Foreign government bonds |  |
Schedule of Investments [Line Items] |  |
Amortized Cost, net | 14.1 | 14.1
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | 0.8 | 1.0
Fair Value | 13.3 | 13.1
Corporate bonds |  |
Schedule of Investments [Line Items] |  |
Amortized Cost, net | 1,955.1 | 1,995.2
Gross Unrealized Gains | 24.2 | 17.3
Gross Unrealized Losses | 208.5 | 230.1
Fair Value | 1,770.8 | 1,782.4
Other asset-backed securities |  |
Schedule of Investments [Line Items] |  |
Amortized Cost, net | 1,570.3 | 1,339.7
Gross Unrealized Gains | 12.5 | 10.8
Gross Unrealized Losses | 34.6 | 22.3
Fair Value | $ 1,548.2 | $ 1,328.2

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