Loans and Allowance for Credit Losses - Loans modified by class and modification type (Detail) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2023	Sep. 30, 2023
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 1,441	$ 2,946
Financing Receivable, Percent Past Due		0.40%	0.80%
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 114	$ 249
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		$ 435	$ 536
Financing Receivable, Percent Past Due		0.80%	1.00%
Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 65	$ 259
Financing Receivable, Percent Past Due		0.10%	0.20%
Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 117	$ 269
Financing Receivable, Percent Past Due		0.40%	1.00%
Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 53	$ 141
Financing Receivable, Percent Past Due		0.10%	0.30%
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 784	$ 1,454
Financing Receivable, Percent Past Due		0.20%	0.40%
Loans purchased from GNMA mortgage pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 657	$ 1,492
Financing Receivable, Percent Past Due		0.60%	1.30%
Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		$ 135	$ 310
Contractual Interest Rate Reduction [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		16	36
Contractual Interest Rate Reduction [Member] | Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		117	268
Contractual Interest Rate Reduction [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		2	6
Contractual Interest Rate Reduction [Member] | Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		135	310
Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		525	1,262
Payment Deferral [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		58	221
Payment Deferral [Member] | Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period			1
Payment Deferral [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		12	20
Payment Deferral [Member] | Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		70	242
Payment Deferral [Member] | Loans purchased from GNMA mortgage pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		455	1,020
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		644	1,085
Extended Maturity [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		98	213
Extended Maturity [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		426	527
Extended Maturity [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		6	21
Extended Maturity [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		39	113
Extended Maturity [Member] | Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		569	874
Extended Maturity [Member] | Loans purchased from GNMA mortgage pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period		75	211
Multiple Modification [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	137	289
Multiple Modification [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	9	9
Multiple Modification [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1],[2]	1	17
Multiple Modification [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]		2
Multiple Modification [Member] | Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1]	10	28
Multiple Modification [Member] | Loans purchased from GNMA mortgage pools [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	[1],[2]	$ 127	$ 261

[1] Includes $126 million of total loans receiving a payment delay and term extension, $9 million of total loans receiving an interest rate reduction and term extension and $2 million of total loans receiving an interest rate reduction, payment delay and term extension for three months ended September 30, 2023. Includes $268 million of total loans receiving a payment delay and term extension, $14 million of total loans receiving an interest rate reduction and term extension and $7 million of total loans receiving an interest rate reduction, payment delay and term extension for nine months ended September 30, 2023.

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