Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	$ 553,375		$ 553,905
Liabilities related to consolidated VIEs	501,067		500,180
Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Federal and state income tax credits recognized in tax expense	133	$ 150
Expense related to investments	126	142
Investment tax credits	37	99
Expenses related to investments recognized in tax expense	92	101
Financial Support Waived Fees [Member]
Variable Interest Entity [Line Items]
Financial or other support to money market funds	47	$ 8
Variable Interest Entity Not Primary Beneficiary [Member] | Private Investment Funds and Partnerships [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	58		57
Assets related to consolidated VIEs	35		35
Variable Interest Entity Not Primary Beneficiary [Member] | Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	10,903		11,219
Assets related to consolidated VIEs	5,161		5,378
Liabilities related to consolidated VIEs	2,236		2,334
Variable Interest Entity Not Primary Beneficiary [Member] | Minimum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	1
Variable Interest Entity Not Primary Beneficiary [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs			78
Variable Interest Entity Primary Beneficiary [Member] | Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	4,800		4,900
Liabilities related to consolidated VIEs	3,600		3,700
Variable Interest Entity Primary Beneficiary [Member] | Tender Option Bond Program [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	1,700		2,400
Liabilities related to consolidated VIEs	$ 1,200		$ 1,500