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Investments - Aging of Unrealized Losses on Investments in Fixed Maturities (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Unrealized Losses |  |
12 Months or Longer |  | $ (0.8)
United States Government and Government Agencies and Authorities |  |
Fair Value |  |
Less Than 12 Months | $ 41.7 | 52.0
12 Months or Longer | 383.6 | 401.6
Total | 425.3 | 453.6
Unrealized Losses |  |
Less Than 12 Months | (0.5) | (0.8)
12 Months or Longer | (101.9) | (83.7)
Total | (102.4) | (84.5)
States and Political Subdivisions |  |
Fair Value |  |
Less Than 12 Months | 242.7 | 112.9
12 Months or Longer | 933.4 | 928.3
Total | 1,176.1 | 1,041.2
Unrealized Losses |  |
Less Than 12 Months | (10.3) | (2.3)
12 Months or Longer | (215.1) | (187.5)
Total | (225.4) | (189.8)
Foreign Governments |  |
Fair Value |  |
Less Than 12 Months | 0.0 | 0.0
12 Months or Longer | 1.4 | 1.9
Total | 1.4 | 1.9
Unrealized Losses |  |
Less Than 12 Months | 0.0 | 0.0
12 Months or Longer | (0.2) | (0.6)
Total | (0.2) | (0.6)
Bonds and Notes |  |
Fair Value |  |
Less Than 12 Months | 674.3 | 198.4
12 Months or Longer | 2,605.7 | 2,813.0
Total | 3,280.0 | 3,011.4
Unrealized Losses |  |
Less Than 12 Months | (40.9) | (5.5)
12 Months or Longer | (477.9) | (378.3)
Total | (518.8) | (383.8)
Redeemable Preferred Stocks |  |
Fair Value |  |
Less Than 12 Months | 2.0 | 0.0
12 Months or Longer | 6.6 | 7.9
Total | 8.6 | 7.9
Unrealized Losses |  |
Less Than 12 Months | 0.0 | 0.0
12 Months or Longer | (1.0) |
Total | (1.0) | (0.8)
Collateralized Loan Obligations |  |
Fair Value |  |
Less Than 12 Months | 34.2 | 38.8
12 Months or Longer | 89.5 | 747.7
Total | 123.7 | 786.5
Unrealized Losses |  |
Less Than 12 Months | (0.1) | (0.4)
12 Months or Longer | (7.1) | (24.1)
Total | (7.2) | (24.5)
Other Mortgage- and Asset-backed |  |
Fair Value |  |
Less Than 12 Months | 12.0 | 15.7
12 Months or Longer | 261.7 | 287.3
Total | 273.7 | 303.0
Unrealized Losses |  |
Less Than 12 Months | (0.1) | (0.1)
12 Months or Longer | (34.4) | (46.2)
Total | (34.5) | (46.3)
Investments in Fixed Maturities |  |
Fair Value |  |
Less Than 12 Months | 1,006.9 | 417.8
12 Months or Longer | 4,281.9 | 5,187.7
Total | 5,288.8 | 5,605.5
Unrealized Losses |  |
Less Than 12 Months | (51.9) | (9.1)
12 Months or Longer | (837.6) | (721.2)
Total | $ (889.5) | $ (730.3)

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