Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	$ (40)	$ (51)
Gain (Loss) on Hedged Items	63	77
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(590)	(249)
Gain (Loss) on Hedged Items	561	240
Net Ineffective Gain (Loss) Recognized - Other Income	(29)	(9)
Available-for-sale Securities [Member] | Interest Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(48)	(54)
Gain (Loss) on Hedged Items	93	88
Available-for-sale Securities [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(656)	(249)
Gain (Loss) on Hedged Items	626	240
Net Ineffective Gain (Loss) Recognized - Other Income	(30)	(9)
Subordinated Debt [Member] | Interest Expense [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	8	3
Gain (Loss) on Hedged Items	(30)	(11)
Subordinated Debt [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	66	0
Gain (Loss) on Hedged Items	(65)	0
Net Ineffective Gain (Loss) Recognized - Other Income	$ 1	$ 0