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Investment Securities - Common Equity Securities and Other Long Term Investments (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Common equity securities |  |
Cost or Amortized Cost | $ 483.5 | $ 660.6
Gross Unrealized Gains | 62.3 | 26.7
Gross Unrealized Losses | (1.2) | (8.4)
Net Foreign Currency Gains (Losses) | (6.2) | (10.5)
Carrying Value | 538.4 | 668.4
Other long-term investments |  |
Cost or Amortized Cost | 1,655.7 | 1,340.8
Gross Unrealized Gains | 446.3 | 271.1
Gross Unrealized Losses | (94.5) | (107.1)
Net Foreign Currency Gains (Losses) | (9.3) | (16.8)
Carrying Value | 1,998.2 | 1,488.0
MediaAlpha |  |
Investment in MediaAlpha |  |
Cost or Amortized Cost | 59.2 | 0.0
Gross Unrealized Gains | 195.7 | 168.6
Gross Unrealized Losses | 0.0 | 0.0
Net Foreign Currency Gains (Losses) | 0.0 | 0.0
Carrying Value | $ 254.9 | $ 168.6

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