Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	$ (51)	$ (60)
Gain (Loss) on Hedged Items	77	87
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(249)	(220)
Gain (Loss) on Hedged Items	240	214
Net Ineffective Gain (Loss) Recognized - Other Income	(9)	(6)
Available-for-sale Securities [Member] | Interest Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(54)	(64)
Gain (Loss) on Hedged Items	88	102
Available-for-sale Securities [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(249)	(219)
Gain (Loss) on Hedged Items	240	213
Net Ineffective Gain (Loss) Recognized - Other Income	(9)	(6)
Subordinated Debt [Member] | Interest Expense [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	3	4
Gain (Loss) on Hedged Items	(11)	(15)
Subordinated Debt [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	0	(1)
Gain (Loss) on Hedged Items	0	1
Net Ineffective Gain (Loss) Recognized - Other Income	$ 0	$ 0