Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended
	Feb. 29, 2024	Mar. 31, 2024	Dec. 31, 2023
Loss Contingencies [Line Items]
Commitments to extend credit to commercial customers		$ 12,400	$ 12,300
Maximum credit risk for recourse associated with loans sold under Federal National Mortgage Association Delegated Underwriting and Servicing program		4,000	3,900
Estimate assessed losses	$ 20,400	1,700
Estimate assessed losses increase	4,100
Estimated uninsured deposits	$ 16,300
Loss contingency expense amount		29	197
Accrued liability		226	$ 197
Minimum [Member]
Loss Contingencies [Line Items]
Range of reasonably possible losses		0
Maximum [Member]
Loss Contingencies [Line Items]
Range of reasonably possible losses		$ 25