Loans and Allowance for Credit Losses - Loans Modified by Class and Delinquency Status (Detail) (parenthetical) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($)
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	$ 717
Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	332	[1]
Financing Receivables 30 To 89 Days Past Due [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period excluding forbearance	40
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	3	[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	86
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	10	[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	32
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	$ 1,000

[1] At March 31, 2023, $32 million of loans 30-89 days past due and $1 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.