Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	$ (43)	$ (62)	$ (94)	$ (121)
Gain (Loss) on Hedged Items	71	95	148	182
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	441	(188)	193	(408)
Gain (Loss) on Hedged Items	(425)	189	(185)	402
Net Ineffective Gain (Loss) Recognized - Other Income	16	1	8	(6)
Available-for-sale Securities [Member] | Interest Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(49)	(64)	(103)	(127)
Gain (Loss) on Hedged Items	93	96	181	198
Available-for-sale Securities [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	453	(188)	205	(407)
Gain (Loss) on Hedged Items	(437)	189	(197)	401
Net Ineffective Gain (Loss) Recognized - Other Income	16	1	8	(6)
Subordinated Debt [Member] | Interest Expense [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	6	2	9	6
Gain (Loss) on Hedged Items	(22)	(1)	(33)	(16)
Subordinated Debt [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(12)	0	(12)	(1)
Gain (Loss) on Hedged Items	12	0	12	1
Net Ineffective Gain (Loss) Recognized - Other Income	$ 0	$ 0	$ 0	$ 0