Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets related to consolidated VIEs	$ 558,886		$ 558,886		$ 553,905
Liabilities related to consolidated VIEs	505,212		505,212		500,180
Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Federal and state income tax credits recognized in tax expense	110	$ 145	243	$ 295
Expense related to investments	106	145	232	287
Investment tax credits	123	90	160	189
Expenses related to investments recognized in tax expense	87	99	179	200
Financial Support Waived Fees [Member]
Variable Interest Entity [Line Items]
Financial or other support to money market funds	70	$ 13	117	$ 21
Variable Interest Entity Not Primary Beneficiary [Member] | Private Investment Funds and Partnerships [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	80		80		57
Assets related to consolidated VIEs	39		39		35
Variable Interest Entity Not Primary Beneficiary [Member] | Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	10,579		10,579		11,219
Assets related to consolidated VIEs	5,012		5,012		5,378
Liabilities related to consolidated VIEs	2,257		2,257		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	75		75		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	3,700		3,700		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