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Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	Mar. 31, 2018 USD ($) fund	Dec. 31, 2017 USD ($)
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments	1
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments	10
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 | $	$ 56.4	$ 54.9

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- Definition

Number of investments held.

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- Definition

The largest investment which the entity has made in a single fund.

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