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Investment Securities (Other Long-Term Investments) (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Investment securities |  |
Other Investments | $ 622.8 | $ 165.7
Kudu investments |  |
Investment securities |  |
Other Investments | 266.5 | 0.0
MediaAlpha |  |
Investment securities |  |
Other Investments | 180.0 | 0.0
DavidShield & PassportCard |  |
Investment securities |  |
Other Investments | 90.0 | 75.0
Elementum Holdings, L.P. |  |
Investment securities |  |
Other Investments | 55.1 | 0.0
Other unconsolidated private equity investments, at fair value |  |
Investment securities |  |
Other Investments | 31.2 | 60.0
Kudu |  |
Investment securities |  |
Other Investments | 0.0 | 30.7
Hedge Funds and Private Equity Funds |  |
Investment securities |  |
Other Investments | 161.1 | 146.1
Insurance-linked securities funds |  |
Investment securities |  |
Other Investments | 41.2 | 0.0
Other long-term investments |  |
Investment securities |  |
Other Investments | 31.2 | 13.8
White Mountains |  |
Investment securities |  |
Other Investments | $ 856.3 | $ 325.6

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