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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, 2022 | Dec. 31, 2021
Common equity securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | $ 274.3 | $ 236.3
Gross Unrealized Gains | 20.8 | 16.1
Gross Unrealized Losses | (1.9) | 0.0
Net Foreign Currency Gains (Losses) | (3.1) | (1.3)
Common equity securities, at fair value | 290.1 | 251.1
Marketing Technology (MediaAlpha) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | 0.0 | 0.0
Gross Unrealized Gains | 280.4 | 261.6
Gross Unrealized Losses | 0.0 | 0.0
Net Foreign Currency Gains (Losses) | 0.0 | 0.0
Common equity securities, at fair value | 280.4 | 261.6
Other long-term investments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | 1,187.0 | 1,186.7
Gross Unrealized Gains | 291.6 | 239.0
Gross Unrealized Losses | (52.8) | (44.1)
Net Foreign Currency Gains (Losses) | 2.7 | (3.8)
Common equity securities, at fair value | $ 1,428.5 | $ 1,377.8

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