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Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions | Mar. 31, 2017 USD ($) fund | Dec. 31, 2016 USD ($)
--- | --- | ---
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Other Investments | $ | $ 331.7 | $ 323.3
Hedge funds |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Number of investments | fund | 5 |
Private equity funds |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Number of investments | fund | 20 |
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 | $ | $ 54.2 | $ 36.5

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