XML 122 R103.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Commitments, Contingencies and Guarantees - Additional Information (Detail) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 USD ($) attorney_general
Loss Contingencies [Line Items] |
Contractual obligation | $ 2,000
Other liabilities reserve | $ 2
Loss emergence period | 1 year
Washington and Pennsylvania |
Loss Contingencies [Line Items] |
Number of state attorneys general | attorney_general | 3

X
- Definition Loss Contingency, Loss Emergence Period + References No definition available. + Details
Name: | slm_LossContingencyLossEmergencePeriod
Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of Attorneys General + References No definition available. + Details
Name: | slm_NumberofAttorneysGeneral
Namespace Prefix: | slm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Other Liabilities Reserve + References No definition available. + Details
Name: | slm_OtherLiabilitiesReserve
Namespace Prefix: | slm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments. + References No definition available. + Details
Name: | us-gaap_ContractualObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_StatementGeographicalAxis=slm_WashingtonandPennsylvaniaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |