Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	Jun. 30, 2017 USD ($) fund	Dec. 31, 2016 USD ($)
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments	2
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments	8
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 | $	$ 53.8	$ 21.5