Allowance for Loan Losses - Accrued Interest Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Total Interest Receivable	$ 1,168,823	$ 951,138
Greater Than 90 Days Past Due	1,920	1,372
Allowance for Uncollectible Interest	$ 6,322	$ 4,664

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