Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income) (Details) - Client Related and Trading - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	$ 67.9	$ 47.0	$ 222.2	$ 154.0
Foreign Exchange Contracts | Foreign Exchange Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	62.9	46.4	209.3	149.4
Interest Rate Contracts | Security Commissions and Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	$ 5.0	$ 0.6	$ 12.9	$ 4.6