Allowance for Credit Losses - Accrued Interest Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Receivables [Abstract]
Total Interest Receivable	$ 1,454,176	$ 1,366,158
Greater Than 90 Days Past Due	4,096	2,390
Allowance for Uncollectible Interest	$ 4,427	$ 5,309

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