Allowance for Loan Losses - Loan Type (Detail) - FFELP Loans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable Recorded Investment Past Due [Line Items]
Total loans, gross	$ 28,314	$ 31,032	$ 38,140
Change	(2,718)
Stafford Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total loans, gross	9,290	9,966
Change	(676)
Consolidation Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total loans, gross	16,151	17,956
Change	(1,805)
Rehab Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total loans, gross	2,873	$ 3,110
Change	$ (237)