Derivative Financial Instruments - Impact of Derivatives on Consolidated Statement of Income (Details) - Derivatives not designated as hedging instruments - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	$ 165	$ 143	$ 371	$ 276
Foreign exchange contracts | Trading services
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	165	144	369	278
Interest-rate contracts | Trading services
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(1)	(1)	(1)	(1)
Other Derivative Contracts | Trading services
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	1	0	3	0
Other Derivative Contracts | Processing Fees And Other Revenue
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	0	0	0	(1)
Other Derivative Contracts | Compensation and Employee Benefits
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	$ 33	$ (22)	$ 92	$ (70)