Loans and Allowance for Credit Losses - Loans modified by class and modification type (Detail) (Parenthetical) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023
Financing Receivable, Modifications [Line Items]
Loans modified during the period	$ 1,123	$ 1,879
Payment Deferral And Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	100	151
Contractual Interest Rate Reduction And Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	2	5
Contractual Interest Rate Reduction Extended Maturity And Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Loans modified during the period	$ 1	$ 6