Loans and Allowance for Credit Losses - Loans Modified by Class and Delinquency Status (Detail) (parenthetical) $ in Millions	6 Months Ended
	Jun. 30, 2023 USD ($)
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	$ 1,368
Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	692	[1]
Financing Receivables 30 To 89 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	55
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	11	[1]
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	122
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	13	[1]
Government National Mortgage Association [Member] | 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	95
Government National Mortgage Association [Member] | 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	$ 20

[1] At June 30, 2023, $95 million of loans 30-89 days past due and $20 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.