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, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Derivative [Line Items]
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	$ 2,605	$ 2,485
Cash Flow Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	20	(13)
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	(1)	(1)
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	2	2
Interest-rate contracts | Net interest revenue | Cash Flow Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	0	(1)
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	(1)	(1)
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	0	1
Foreign exchange contracts | Net interest revenue | Cash Flow Hedges
Derivative [Line Items]
Amount of Gain (Loss) on Derivative Recognized in Other Comprehensive Income	20	(12)
Amount of Gain (Loss) Reclassified from OCI to Consolidated Statement of Income	0	0
Amount of Gain (Loss) on Derivative Recognized in Consolidated Statement of Income	$ 2	$ 1