Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Minimum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	$ 1		$ 1		$ 1
Maximum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	50		50		53
Conduit [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	34		34		35
Tender Option Bond Program [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	2,300		2,300		2,900
Liabilities related to consolidated VIEs	2,200		2,200		2,700
Community Development and Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Federal and state income tax credits recognized in tax expense	170	$ 179	338	$ 357
Expense related to investments	156	166	302	330
Expenses related to investments recognized in tax expense	65	59	131	130
Investment tax credits	170	$ 217	284	$ 320
Investment carrying amount	4,995		4,995		4,259
Maximum exposure to loss	8,608		8,608		8,393
Assets related to consolidated VIEs	2,900		2,900		2,700
Liabilities related to consolidated VIEs	2,100		2,100		2,000
Private Investment Funds and Partnerships [Member]
Variable Interest Entity [Line Items]
Investment carrying amount	86		86		97
Maximum exposure to loss	$ 95		$ 95		$ 105