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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	$ 56.2	$ 67.9	$ 188.2	$ 222.2
Foreign Exchange Contracts | Foreign Exchange Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	53.6	62.9	178.5	209.3
Interest Rate Contracts | Security Commissions and Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	$ 2.6	$ 5.0	$ 9.7	$ 12.9