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Commitments, Contingencies and Guarantees - Additional Information (Detail) (USD $) | Sep. 29, 2014
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Commitments and Contingencies Disclosure [Abstract] |
FDIC civil monetary penalties | $ 3,300,000 slm_FDICcivilmonetarypenalties
Maximum [Member] |
Loss Contingencies [Line Items] |
Contingency refund | $ 30,000,000 slm_Contingencyrefund / us-gaap_RangeAxis = us-gaap_MaximumMember

X
- Definition Contingency refund + References No definition available. + Details
Name: | slm_Contingencyrefund
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition FDIC civil monetary penalties + References No definition available. + Details
Name: | slm_FDICcivilmonetarypenalties
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |