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Investment Securities - Investment Holding Common Equities/ Other Investments/ MediaAlpha (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2021 | Dec. 31, 2020
Common equity securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | $ 136.4 |
Gross Unrealized Gains | 6.0 |
Gross Unrealized Losses | 0.0 |
Net Foreign Currency (Losses) Gains | (0.4) |
Common equity securities, at fair value | 142.0 |
Marketing Technology (MediaAlpha) |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | 0.0 | $ 0.0
Gross Unrealized Gains | 713.2 | 802.2
Gross Unrealized Losses | 0.0 | 0.0
Net Foreign Currency (Losses) Gains | 0.0 | 0.0
Common equity securities, at fair value | 713.2 | 802.2
Other long-term investments |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Cost or Amortized Cost | 979.0 | 767.4
Gross Unrealized Gains | 166.1 | 95.8
Gross Unrealized Losses | (64.6) | (78.1)
Net Foreign Currency (Losses) Gains | 0.9 | 1.7
Common equity securities, at fair value | $ 1,081.4 | $ 786.8

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