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Education Loans - Schedule of Loans Carried under Fair Value Option (Parenthetical) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	$ 1,671		$ 1,671		$ 1,658
Write-offs	(79)	$ (121)	(271)	$ (310)
In School Private Education Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable	2		2
Legacy Private Education Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Write-offs	(121)		(121)
Classified held for sale	$ 1,400		$ 1,400