Allowance for Loan Losses - Accrued Interest Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Total Interest Receivable	$ 951,138	$ 739,847
Greater Than 90 Days Past Due	1,372	845
Allowance for Uncollectible Interest	$ 4,664	$ 2,898

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