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Loans Held for Investment - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Jul. 01, 2006	Jun. 30, 2006	Sep. 30, 1993
Receivables [Abstract]
Percent of Private Loans indexed to LIBOR	82.00%slm_PercentofPrivateLoansindexedtoLIBOR
Tier One of Government Guarantee	97.00%slm_TierOneofGovernmentGuarantee		97.00%slm_TierOneofGovernmentGuarantee
Tier Two of Government Guarantee				98.00%slm_TierTwoofGovernmentGuarantee
Tier 3 of Government Guarantee					100.00%slm_TierThreeofGovernmentGuarantee
Estimated weighted average life of student loans	6 years 5 months 6 days	6 years 2 months 6 days