Derivative Financial Instruments - Impact of Derivatives on Consolidated Statement of Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Derivatives not designated as hedging instruments
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	$ 207	$ 133
Compensation and Employee Benefits | Derivatives not designated as hedging instruments
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	59	49
Foreign exchange contracts | Trading services | Derivatives not designated as hedging instruments
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	204	134
Interest-rate contracts | Processing fees and other revenue | Derivatives not designated as hedging instruments
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	1	0
Other derivative contracts | Trading services | Derivatives not designated as hedging instruments
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	2	(1)
Other derivative contracts | Compensation and Employee Benefits | Derivatives not designated as hedging instruments
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	59	49
Fair Value Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(24)	79
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	27	(75)
Fair Value Hedges | Foreign exchange contracts | Processing fees and other revenue
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(67)	42
Fair Value Hedges | Foreign exchange contracts | Processing fees and other revenue | Investment securities
Derivative [Line Items]
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	67	(42)
Fair Value Hedges | Interest-rate contracts | Processing fees and other revenue | Contract one
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(25)	(12)
Fair Value Hedges | Interest-rate contracts | Processing fees and other revenue | Contract two
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	68	49
Fair Value Hedges | Interest-rate contracts | Processing fees and other revenue | Long-term debt
Derivative [Line Items]
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	25	12
Fair Value Hedges | Interest-rate contracts | Processing fees and other revenue | Investment securities available for sale
Derivative [Line Items]
Amount of Gain (Loss) on Hedged Item Recognized in Consolidated Statement of Income	$ (65)	$ (45)