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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	$ 567,495		$ 567,495		$ 553,905
Liabilities related to consolidated VIEs	513,117		513,117		500,180
Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Federal and state income tax credits recognized in tax expense	113	$ 142	356	$ 437
Expense related to investments	101	142	333	429
Investment tax credits	75	118	235	307
Expenses related to investments recognized in tax expense	83	97	262	297
Financial Support Waived Fees [Member]
Variable Interest Entity [Line Items]
Financial or other support to money market funds	67	$ 28	184	$ 49
Variable Interest Entity Not Primary Beneficiary [Member] | Private Investment Funds and Partnerships [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	81		81		57
Assets related to consolidated VIEs	40		40		35
Variable Interest Entity Not Primary Beneficiary [Member] | Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	10,368		10,368		11,219
Assets related to consolidated VIEs	4,865		4,865		5,378
Liabilities related to consolidated VIEs	2,180		2,180		2,334
Variable Interest Entity Not Primary Beneficiary [Member] | Minimum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	1		1		1
Variable Interest Entity Not Primary Beneficiary [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Aggregate amount of investments in unconsolidated VIEs	71		71		78
Variable Interest Entity Primary Beneficiary [Member] | Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	5,100		5,100		4,900
Liabilities related to consolidated VIEs	3,600		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		1,700		2,400
Liabilities related to consolidated VIEs	$ 1,200		$ 1,200		$ 1,500