Loans and Allowance for Credit Losses - Loans modified by class and modification type (Detail) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
		Jun. 30, 2023	Jun. 30, 2023
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 1,123	$ 1,879
Financing Receivable, Percent Past Due		0.30%	0.50%
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 149	$ 318
Financing Receivable, Percent Past Due		0.10%	0.20%
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 101	$ 109
Financing Receivable, Percent Past Due		0.20%	0.20%
Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	$ 89	$ 233
Financing Receivable, Percent Past Due	[1]	0.10%	0.20%
Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 91	$ 174
Financing Receivable, Percent Past Due		0.30%	0.70%
Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 56	$ 106
Financing Receivable, Percent Past Due		0.10%	0.20%
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 486	$ 940
Financing Receivable, Percent Past Due		0.10%	0.20%
Loans Excluding Loans Purchased From Government National Mortgage Association Mortgage pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	$ 637	$ 939
Financing Receivable, Percent Past Due	[1]	0.60%	0.80%
Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 106	$ 337
Contractual Interest Rate Reduction [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		13	159
Contractual Interest Rate Reduction [Member] | Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		91	174
Contractual Interest Rate Reduction [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		2	4
Contractual Interest Rate Reduction [Member] | Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		106	337
Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		546	869
Payment Deferral [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	79	202
Payment Deferral [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		14	18
Payment Deferral [Member] | Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		93	220
Payment Deferral [Member] | Loans Excluding Loans Purchased From Government National Mortgage Association Mortgage pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	453	649
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		368	511
Extended Maturity [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		136	159
Extended Maturity [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		101	109
Extended Maturity [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	6	15
Extended Maturity [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		39	81
Extended Maturity [Member] | Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		282	364
Extended Maturity [Member] | Loans Excluding Loans Purchased From Government National Mortgage Association Mortgage pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	86	147
Multiple Modification [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[2]	103	162
Multiple Modification [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1],[2]	4	16
Multiple Modification [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[2]	1	3
Multiple Modification [Member] | Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[2]	5	19
Multiple Modification [Member] | Loans Excluding Loans Purchased From Government National Mortgage Association Mortgage pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1],[2]	$ 98	$ 143

[1] Percent of class total amounts expressed as a percent of total residential mortgage loan balances.

[2] Includes $100 million of total loans receiving a payment delay and term extension, $2 million of total loans receiving an interest rate reduction and term extension and $1 million of total loans receiving an interest rate reduction, payment delay and term extension for three months ended ended June 30, 2023. Includes $151 million of total loans receiving a payment delay and term extension, $5 million of total loans receiving an interest rate reduction and term extension and $6 million of total loans receiving an interest rate reduction, payment delay and term extension for six months ended ended June 30, 2023.