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Investment Securities (Other long-term investments) (Details) - USD ($) $ in Millions | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Other Investments | $ 229.6 | $ 172.8
Hedge and private equity funds included in other long-term investments |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Other Investments | 154.9 | 82.6
Limited liability companies and private equity securities |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Other Investments | 59.1 | 57.6
Convertible Preferred Stock |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Other Investments | 27.2 | 30.6
Forward Contracts |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Other Investments | (15.4) | (1.2)
Other long-term investments |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Other Investments | $ 3.8 | $ 3.2
OneTitle |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Ownership interest (as a percent) | 20.00% |
Surplus notes | $ 10.0 |

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