Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Loss Contingencies [Line Items]
Commitments to extend credit to commercial customers	$ 12,700	$ 12,300
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program	4,200	3,900
Estimate assessed losses	34	197
Loss contingency accrual	157	$ 197
Minimum
Loss Contingencies [Line Items]
Range of reasonably possible losses	0
Maximum
Loss Contingencies [Line Items]
Range of reasonably possible losses	$ 25