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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 |  |  |

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- Definition Estimated weighted average life of student loans. + References No definition available. + Details
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- Definition Percent of Private Loans indexed to LIBOR + References No definition available. + Details
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- Definition Tier One of Government Guarantee + References No definition available. + Details
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- Definition Tier Three of Government Guarantee + References No definition available. + Details
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- Definition Tier Two of Government Guarantee + References No definition available. + Details
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- Details
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