Loans and Allowance for Credit Losses - Loans Modified by Class and Delinquency Status (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	$ 2,299
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	248
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	537
Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	1,118	[1]
Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	268
Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	128
Financial Asset, Not Past Due [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	1,957
Financial Asset, Not Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	223
Financial Asset, Not Past Due [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	347
Financial Asset, Not Past Due [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	1,089	[1]
Financial Asset, Not Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	192
Financial Asset, Not Past Due [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	106
Financing Receivables 30 To 89 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	96
Financing Receivables 30 To 89 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	11
Financing Receivables 30 To 89 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	1
Financing Receivables 30 To 89 Days Past Due [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	15	[1]
Financing Receivables 30 To 89 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	54
Financing Receivables 30 To 89 Days Past Due [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	15
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	246
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	14
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	189
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	14	[1]
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	22
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Other Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	$ 7

[1] At September 30, 2023, $263 million of loans 30-89 days past due and $64 million of loans 90 days or more past due purchased and that could be purchased from GNMA mortgage pools under delinquent loan repurchase options whose payments are insured by the Federal Housing administration or guaranteed by the United States Department of Veterans Affairs, were classified as current.