Commitments, Contingencies and Guarantees - Additional Information (Detail)		1 Months Ended	3 Months Ended
	Apr. 12, 2023 USD ($)	Jan. 31, 2022 StateAttorneysGeneral	Mar. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)
Loss Contingencies [Line Items]
Accrued probable incurred loss				$ 45,000,000
Number of State Attorneys General under Agreement | StateAttorneysGeneral		40
Additional private loan provision for loan losses			$ 23,000,000
Aggregate cash fund contribution	$ 44,000,000
Net impact to operating expense			$ 0
Minimum [Member]
Loss Contingencies [Line Items]
Accrued probable incurred loss				0
Maximum [Member]
Loss Contingencies [Line Items]
Accrued probable incurred loss				250,000,000
SLM BankCo [Member] | Indemnification Matters [Member]
Loss Contingencies [Line Items]
Accrued liabilities related to indemnification matters				$ 0