Derivative Financial Instruments - Gains and Losses on Hedged Items in Fair Value Hedges (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	$ (237)	$ (186)
Gain (Loss) on Hedged Items	353	366
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(688)	819
Gain (Loss) on Hedged Items	672	(799)
Net Ineffective Gain (Loss) Recognized - Other Income	(16)	20
Available-for-sale Securities [Member] | Interest Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(246)	(202)
Gain (Loss) on Hedged Items	375	427
Available-for-sale Securities [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(684)	821
Gain (Loss) on Hedged Items	668	(801)
Net Ineffective Gain (Loss) Recognized - Other Income	(16)	20
Commercial Loans [Member] | Interest Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		0
Gain (Loss) on Hedged Items		0
Commercial Loans [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		(2)
Gain (Loss) on Hedged Items		0
Net Ineffective Gain (Loss) Recognized - Other Income		(2)
Subordinated Debt [Member] | Interest Expense [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	9	16
Gain (Loss) on Hedged Items	(22)	(61)
Subordinated Debt [Member] | Other Income [Member] | Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	(4)	0
Gain (Loss) on Hedged Items	4	2
Net Ineffective Gain (Loss) Recognized - Other Income	$ 0	$ 2