Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	$ (59)	$ (52)	$ (181)	$ (156)
Gain (Loss) on Hedged Items	90	97	273	291
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	10	42	(397)	608
Gain (Loss) on Hedged Items	(10)	(38)	392	(592)
Net Ineffective Gain (Loss) Recognized - Other Income	0	4	(5)	16
Available-for-sale Securities [Member] | Interest Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(61)	(56)	(188)	(168)
Gain (Loss) on Hedged Items	90	112	289	337
Available-for-sale Securities [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	10	42	(396)	609
Gain (Loss) on Hedged Items	(10)	(39)	391	(593)
Net Ineffective Gain (Loss) Recognized - Other Income	0	3	(5)	16
Subordinated Debt [Member] | Interest Expense [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	2	4	7	12
Gain (Loss) on Hedged Items	0	(15)	(16)	(46)
Subordinated Debt [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	0	0	(1)	(1)
Gain (Loss) on Hedged Items	0	1	1	1
Net Ineffective Gain (Loss) Recognized - Other Income	$ 0	$ 1	$ 0	$ 0