Derivative Financial Instruments - Schedule of Differences Between the Gains (Losses) on the Derivative and The Gains (Losses) on the Hedged Item (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative [Line Items]
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	$ 2,619	$ 2,582	$ 7,838	$ 7,665
Other Comprehensive Income (Loss), Change in Unrealized Gain Loss on AFS Securities Designated as Fair Value Hedges, Net of Related Taxes	16	(14)	9	9
Derivatives designated as hedging instruments | Fair Value Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	64	(66)	122	49
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(57)	68	(115)	(43)
Derivatives designated as hedging instruments | Cash Flow Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	2	3	6	7
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	40	91	81	25
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	(1)	(1)	(3)	(3)
Derivatives designated as hedging instruments | Foreign exchange contracts | Net interest revenue | Cash Flow Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	2	2	6	4
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	40	92	81	28
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	0	0	0	0
Derivatives designated as hedging instruments | Interest-rate contracts | Net interest revenue | Cash Flow Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	0	1	0	3
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	0	(1)	0	(3)
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	(1)	(1)	(3)	(3)
Investment securities available for sale | Derivatives designated as hedging instruments | Foreign exchange contracts | Processing Fees And Other Revenue | Fair Value Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(80)	(82)	(132)	(22)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	80	82	132	22
Investment securities available for sale | Derivatives designated as hedging instruments | Interest-rate contracts | Processing Fees And Other Revenue | Fair Value Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(25)	24	(13)	(17)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	26	(23)	14	15
Deposits | Derivatives designated as hedging instruments | Foreign exchange contracts | Processing Fees And Other Revenue | Fair Value Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(13)		102
Gain (Loss) on Fair Value Hedges Recognized in Earnings	13		(102)
Long-term debt | Derivatives designated as hedging instruments | Interest-rate contracts | Processing Fees And Other Revenue | Fair Value Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	182	(8)	165	88
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ (176)	$ 9	$ (159)	$ (80)