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