Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	$ (44)	$ (59)	$ (138)	$ (181)
Gain (Loss) on Hedged Items	70	90	218	273
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(407)	10	(214)	(397)
Gain (Loss) on Hedged Items	389	(10)	204	392
Net Ineffective Gain (Loss) Recognized - Other Income	(18)	0	(10)	(5)
Available-for-sale Securities [Member] | Interest Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(51)	(61)	(154)	(188)
Gain (Loss) on Hedged Items	92	90	273	289
Available-for-sale Securities [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(434)	10	(229)	(396)
Gain (Loss) on Hedged Items	414	(10)	217	391
Net Ineffective Gain (Loss) Recognized - Other Income	(20)	0	(12)	(5)
Subordinated Debt [Member] | Interest Expense [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	7	2	16	7
Gain (Loss) on Hedged Items	(22)	0	(55)	(16)
Subordinated Debt [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	27	0	15	(1)
Gain (Loss) on Hedged Items	(25)	0	(13)	1
Net Ineffective Gain (Loss) Recognized - Other Income	$ 2	$ 0	$ 2	$ 0