Significant Accounting Policies - Securitization Accounting (Details)	12 Months Ended
Dec. 31, 2020
Accounting Policies [Abstract]
Asset balance related to securitization trust (as a percentage)	10.00%

Variable Interest Entities, Option to Exercise, Maximum Percentage of Assets to Original Loan Balance

No definition available.

Name:	slm_VariableInterestEntitiesOptiontoExerciseMaximumPercentageofAssetstoOriginalLoanBalance
Namespace Prefix:	slm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration