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Investment Securities (Other Long-Term Investments) (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Hedge and private equity funds included in other long-term investments |  |
Investment securities |  |
Other investments | $ 125.3 | $ 82.6
Private equity securities and limited liability companies, at fair value |  |
Investment securities |  |
Other investments | 83.2 | 88.2
Forward Contracts |  |
Investment securities |  |
Other investments | (3.7) | (1.2)
Other long-term investments |  |
Investment securities |  |
Other investments | $ 4.0 | $ 3.2
OneTitle |  |
Investment securities |  |
Ownership interest (as a percent) | 20.00% |
Surplus notes | $ 10.0 |

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