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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative [Line Items]
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	$ 2,614	$ 2,598	$ 5,219	$ 5,083
Other Comprehensive Income (Loss), Change in Unrealized Gain Loss on AFS Securities Designated as Fair Value Hedges, Net of Related Taxes	(22)	13	(7)	23
Derivatives designated as hedging instruments | Fair Value Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	(49)	41	(70)	115
Gain (Loss) on Fair Value Hedges Recognized in Earnings	45	(40)	70	(111)
Derivatives designated as hedging instruments | Cash Flow Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	2	2	4	4
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	21	(53)	41	(66)
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	(1)	(1)	(2)	(2)
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	1	4	2
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	21	(52)	41	(64)
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	2
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	0	(1)	0	(2)
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	(1)	(1)	(2)	(2)
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	12	47	(52)	96
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(12)	(44)	52	(89)
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	37	(24)	(17)	(41)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	(38)	22	(12)	38
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)		(13)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	13		13
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	(85)	18	12	60
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ 82	$ (18)	$ 17	$ (60)