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Investment Securities - Investment Holdings (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023
U.S. Government and agency obligations |  |
Investment securities |  |
Cost or Amortized Cost | $ 461.8 | $ 209.0
Gross Unrealized Gains | 1.1 | 0.3
Gross Unrealized Losses | (0.8) | (4.4)
Net Foreign Currency Gains (Losses) | 0.0 | 0.0
Carrying Value | 462.1 | 204.9
Debt securities issued by corporations |  |
Investment securities |  |
Cost or Amortized Cost | 1,444.5 | 1,085.9
Gross Unrealized Gains | 4.6 | 5.6
Gross Unrealized Losses | (31.4) | (45.4)
Net Foreign Currency Gains (Losses) | (3.5) | (1.1)
Carrying Value | 1,414.2 | 1,045.0
Municipal obligations |  |
Investment securities |  |
Cost or Amortized Cost | 3.2 | 275.1
Gross Unrealized Gains | 0.0 | 0.9
Gross Unrealized Losses | 0.0 | (15.1)
Net Foreign Currency Gains (Losses) | 0.0 | 0.0
Carrying Value | 3.2 | 260.9
Mortgage and asset-backed securities |  |
Investment securities |  |
Cost or Amortized Cost | 400.2 | 417.2
Gross Unrealized Gains | 0.2 | 2.0
Gross Unrealized Losses | (26.5) | (29.8)
Net Foreign Currency Gains (Losses) | 0.0 | 0.0
Carrying Value | 373.9 | 389.4
Collateralized loan obligations |  |
Investment securities |  |
Cost or Amortized Cost | 237.3 | 211.2
Gross Unrealized Gains | 1.2 | 0.4
Gross Unrealized Losses | (0.2) | (2.4)
Net Foreign Currency Gains (Losses) | (1.6) | (0.1)
Carrying Value | 236.7 | 209.1
Foreign government and agency obligations |  |
Investment securities |  |
Cost or Amortized Cost | 22.2 |
Gross Unrealized Gains | 0.0 |
Gross Unrealized Losses | (0.1) |
Net Foreign Currency Gains (Losses) | (0.6) |
Carrying Value | 21.5 |
Fixed maturity investments |  |
Investment securities |  |
Cost or Amortized Cost | 2,569.2 | 2,198.4
Gross Unrealized Gains | 7.1 | 9.2
Gross Unrealized Losses | (59.0) | (97.1)
Net Foreign Currency Gains (Losses) | (5.7) | (1.2)
Carrying Value | $ 2,511.6 | $ 2,109.3

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