Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income) (Details) - Client Related and Trading - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	$ 67.4	$ 77.8	$ 132.0	$ 154.3
Foreign Exchange Contracts | Foreign Exchange Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	64.4	74.8	124.9	146.4
Interest Rate Contracts | Security Commissions and Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	$ 3.0	$ 3.0	$ 7.1	$ 7.9