Allowance for Credit Losses - Accrued Interest Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Receivables [Abstract]
Total Interest Receivable	$ 1,386,427	$ 1,168,895
90 Days and Greater Past Due	3,636	4,354
Allowance for Uncollectible Interest	$ 4,351	$ 4,467

Greater than ninety days past due accrued interest receivable.

No definition available.

Name:	slm_GreaterThanNinetyDaysPastDueAccruedInterestReceivable
Namespace Prefix:	slm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant