Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Minimum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	$ 1,000,000		$ 1,000,000		$ 1,000,000
Maximum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	54,000,000		54,000,000		37,000,000
Conduit [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	114,000,000		114,000,000		116,000,000
Tender Option Bond Program [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	4,100,000,000		4,100,000,000		4,600,000,000
Liabilities related to consolidated VIEs	3,900,000,000		3,900,000,000		4,600,000,000
Community Development and Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Federal and state income tax credits recognized in tax expense	189,000,000	187,000,000	546,000,000	527,000,000
Expense related to investments	187,000,000	247,000,000	517,000,000	686,000,000
Expenses related to investments recognized in tax expense	60,000,000	87,000,000	190,000,000	267,000,000
Investment tax credits	262,000,000	254,000,000	582,000,000	454,000,000
Assets related to consolidated VIEs	2,600,000,000		2,600,000,000		2,500,000,000
Liabilities related to consolidated VIEs	2,000,000,000		2,000,000,000		1,800,000,000
Investment carrying amount	4,385,000,000		4,385,000,000		4,178,000,000
Maximum exposure to loss	8,038,000,000		8,038,000,000		7,390,000,000
Private Investment Funds And Partnerships [Member]
Variable Interest Entity [Line Items]
Investment carrying amount	97,000,000		97,000,000		98,000,000
Maximum exposure to loss	$ 106,000,000		$ 106,000,000		$ 107,000,000