Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 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	52		52		53
Conduit [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	32		32		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	174	$ 189	512	$ 546
Expense related to investments	169	187	471	517
Expenses related to investments recognized in tax expense	67	60	198	190
Investment tax credits	340	$ 262	624	$ 582
Investment carrying amount	5,056		5,056		4,259
Maximum exposure to loss	8,862		8,862		8,393
Assets related to consolidated VIEs	3,000		3,000		2,700
Liabilities related to consolidated VIEs	2,300		2,300		2,000
Private Investment Funds and Partnerships [Member]
Variable Interest Entity [Line Items]
Investment carrying amount	81		81		97
Maximum exposure to loss	$ 96		$ 96		$ 105