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