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Investment Securities - Investment Holding Common Equities/ Other Investments/ MediaAlpha (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2023 | Dec. 31, 2022
Common equity securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | $ 660.6 | $ 660.6
Gross Unrealized Gains | 48.0 | 26.7
Gross Unrealized Losses | (2.8) | (8.4)
Net Foreign Currency Gains (Losses) | (8.0) | (10.5)
Common equity securities, at fair value | 697.8 | 668.4
Marketing Technology (MediaAlpha) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | 0.0 | 0.0
Gross Unrealized Gains | 253.8 | 168.6
Gross Unrealized Losses | 0.0 | 0.0
Net Foreign Currency Gains (Losses) | 0.0 | 0.0
Common equity securities, at fair value | 253.8 | 168.6
Other long-term investments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | 1,489.7 | 1,340.8
Gross Unrealized Gains | 264.3 | 271.1
Gross Unrealized Losses | (96.2) | (107.1)
Net Foreign Currency Gains (Losses) | (14.8) | (16.8)
Common equity securities, at fair value | $ 1,643.0 | $ 1,488.0

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