Loans and Allowance for Credit Losses - Loans modified by class and modification type (Detail) (Parenthetical) - 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
Payment Deferral And Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	126	268
Contractual Interest Rate Reduction And Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	9	14
Contractual Interest Rate Reduction Extended Maturity And Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	$ 2	$ 7