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Asset-Backed Commercial Paper Funding Facility (Details) (Commercial Paper, USD $)
Dec. 31, 2014
Dec. 19, 2014
Commercial Paper
   
Line of Credit Facility [Line Items]    
Asset backed commercial paper student funding facility   $ 750,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= us-gaap_CommercialPaperMember
Percent participation in ABCP 5.00%slm_LineofCreditFacilityPercentOutstandingofBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= us-gaap_CommercialPaperMember
 
Participation in ABCP 37,500,000us-gaap_LinesOfCreditCurrent
/ us-gaap_CreditFacilityAxis
= us-gaap_CommercialPaperMember
 
Asset backed commercial paper remaining borrowing capacity $ 712,500,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= us-gaap_CommercialPaperMember