Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Variable Interest Entity [Line Items]
Realized federal and state income tax credits on investments	$ 441,000,000	$ 227,000,000	$ 981,000,000	$ 581,000,000
Tax advantaged investment costs included in tax expense	132,000,000	123,000,000	512,000,000	316,000,000
Tax advantaged investment costs recognized in income statement	292,000,000	263,000,000	931,000,000	677,000,000
Decrease in other asset as a result of deconsolidation of VIE'S	4,600,000,000
Decrease in long-term debt as a result of deconsolidation of VIE'S	4,600,000,000
Company's investment in unconsolidated VIEs	1,000,000,000		1,000,000,000
Aggregate amount of investments in unconsolidated VIEs	2,700,000,000		2,700,000,000		1,900,000,000
Unfunded capital commitments related to unconsolidated VIEs	1,900,000,000		1,900,000,000		1,300,000,000
Company's maximum exposure to unconsolidated VIEs, including any tax implications	7,200,000,000		7,200,000,000		5,200,000,000
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	40,000,000		40,000,000		58,000,000
Community Development and Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	1,800,000,000		1,800,000,000		7,100,000,000
Liabilities related to consolidated VIEs	434,000,000		434,000,000		5,200,000,000
Aggregate amount of investments in unconsolidated VIEs	2,600,000,000		2,600,000,000		1,800,000,000
Company's maximum exposure previously recorded tax credits	4,500,000,000		4,500,000,000		3,300,000,000
Conduit [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	134,000,000		134,000,000		144,000,000
Tender Option Bond Program [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	4,800,000,000		4,800,000,000		5,300,000,000
Liabilities related to consolidated VIEs	$ 4,700,000,000		$ 4,700,000,000		$ 5,000,000,000