Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2024
Loss Contingencies [Line Items]
Commitments to extend credit to commercial customers	$ 12,400	$ 12,300	$ 12,400
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program	4,000	3,900	4,000
Estimate assessed losses	5	$ 197	34
Minimum
Loss Contingencies [Line Items]
Range of reasonably possible losses	0		0
Maximum
Loss Contingencies [Line Items]
Range of reasonably possible losses	$ 25		$ 25