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Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions | Sep. 30, 2015 USD ($) fund | Jun. 30, 2015 USD ($) | Dec. 31, 2014 USD ($)
--- | --- | --- | ---
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Other Investments | $ 294.6 |  | $ 318.0
Hedge funds |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Number of investments | fund | 10 |  |
Private equity funds |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Number of investments | fund | 22 |  |
Hedge and private equity funds included in other long-term investments |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Largest single fund investment |  | $ 22.3 |

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