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Investments in Unconsolidated Entities (Details) - White Mountains - USD ($) $ in Millions | Jun. 30, 2019 | Dec. 31, 2018
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Investments in unconsolidated affiliates |  |
Other Investments | $ 664.4 | $ 325.6
Equity method eligible private equity securities, at fair value |  |
Investments in unconsolidated affiliates |  |
Other Investments | 262.2 | 138.1
Investments, accounted for under the equity method |  |
Investments in unconsolidated affiliates |  |
Other Investments | 0.7 | 1.3
Total investments in equity method eligible unconsolidated entities |  |
Investments in unconsolidated affiliates |  |
Other Investments | 262.9 | 139.4
Other unconsolidated investments |  |
Investments in unconsolidated affiliates |  |
Other Investments | $ 401.5 | $ 186.2

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