<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.24.3</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>461</ContextCount>
  <ElementCount>570</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>136</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/Coverpage</Role>
      <ShortName>Cover page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>9952151 - Statement - CONSOLIDATED BALANCE SHEETS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CONSOLIDATEDBALANCESHEETSUnaudited</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952152 - Statement - CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CONSOLIDATEDBALANCESHEETSUnauditedParenthetical</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952153 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONSUnaudited</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952154 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMEUnaudited</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952155 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYUnaudited</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952156 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINEQUITYUnauditedParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952157 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952158 - Disclosure - Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/SignificantAccountingPolicies</Role>
      <ShortName>Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952159 - Disclosure - Investments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/Investments</Role>
      <ShortName>Investments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952160 - Disclosure - Loans Held for Investment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/LoansHeldforInvestment</Role>
      <ShortName>Loans Held for Investment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - Loans Held for Sale</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/LoansHeldforSale</Role>
      <ShortName>Loans Held for Sale</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - Allowance for Credit Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLosses</Role>
      <ShortName>Allowance for Credit Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - Unfunded Loan Commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/UnfundedLoanCommitments</Role>
      <ShortName>Unfunded Loan Commitments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - Goodwill and Acquired Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/GoodwillandAcquiredIntangibleAssets</Role>
      <ShortName>Goodwill and Acquired Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/Deposits</Role>
      <ShortName>Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - Borrowings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/Borrowings</Role>
      <ShortName>Borrowings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - Derivative Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstruments</Role>
      <ShortName>Derivative Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>9952168 - Disclosure - Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/StockholdersEquity</Role>
      <ShortName>Stockholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>9952169 - Disclosure - Earnings (Loss) per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/EarningsLossperCommonShare</Role>
      <ShortName>Earnings (Loss) per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9952170 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9952171 - Disclosure - Regulatory Capital</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/RegulatoryCapital</Role>
      <ShortName>Regulatory Capital</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>9952172 - Disclosure - Commitments, Contingencies and Guarantees</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CommitmentsContingenciesandGuarantees</Role>
      <ShortName>Commitments, Contingencies and Guarantees</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9952173 - Disclosure - Subsequent Event</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/SubsequentEvent</Role>
      <ShortName>Subsequent Event</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>995410 - Disclosure - Pay vs Performance Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/PvpDisclosure</Role>
      <ShortName>Pay vs Performance Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9954471 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/SignificantAccountingPoliciesPolicies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/SignificantAccountingPolicies</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9954472 - Disclosure - Investments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/InvestmentsTables</Role>
      <ShortName>Investments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/Investments</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9954473 - Disclosure - Loans Held for Investment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/LoansHeldforInvestmentTables</Role>
      <ShortName>Loans Held for Investment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/LoansHeldforInvestment</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9954474 - Disclosure - Allowance for Credit Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesTables</Role>
      <ShortName>Allowance for Credit Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/AllowanceforCreditLosses</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9954475 - Disclosure - Unfunded Loan Commitments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/UnfundedLoanCommitmentsTables</Role>
      <ShortName>Unfunded Loan Commitments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/UnfundedLoanCommitments</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9954476 - Disclosure - Goodwill and Acquired Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/GoodwillandAcquiredIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Acquired Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/GoodwillandAcquiredIntangibleAssets</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9954477 - Disclosure - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DepositsTables</Role>
      <ShortName>Deposits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/Deposits</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9954478 - Disclosure - Borrowings (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/BorrowingsTables</Role>
      <ShortName>Borrowings (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/Borrowings</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9954479 - Disclosure - Derivative Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstrumentsTables</Role>
      <ShortName>Derivative Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/DerivativeFinancialInstruments</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9954480 - Disclosure - Stockholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/StockholdersEquityTables</Role>
      <ShortName>Stockholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/StockholdersEquity</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9954481 - Disclosure - Earnings (Loss) per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/EarningsLossperCommonShareTables</Role>
      <ShortName>Earnings (Loss) per Common Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/EarningsLossperCommonShare</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9954482 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/FairValueMeasurements</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9954483 - Disclosure - Regulatory Capital (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/RegulatoryCapitalTables</Role>
      <ShortName>Regulatory Capital (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/RegulatoryCapital</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9954484 - Disclosure - Investments - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/InvestmentsNarrativeDetails</Role>
      <ShortName>Investments - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9954485 - Disclosure - Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/InvestmentsAmortizedCostandFairValueofSecuritiesAvailableforSaleDetails</Role>
      <ShortName>Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9954486 - Disclosure - Investments - Gross Unrealized Losses and Fair Value for Mortgage-Backed in Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/InvestmentsGrossUnrealizedLossesandFairValueforMortgageBackedinUnrealizedLossPositionDetails</Role>
      <ShortName>Investments - Gross Unrealized Losses and Fair Value for Mortgage-Backed in Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9954487 - Disclosure - Investments - Maturity Table (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/InvestmentsMaturityTableDetails</Role>
      <ShortName>Investments - Maturity Table (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9954488 - Disclosure - Loans Held for Investment - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/LoansHeldforInvestmentNarrativeDetails</Role>
      <ShortName>Loans Held for Investment - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9954489 - Disclosure - Loans Held for Investment - Student Loan Portfolio by Program (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/LoansHeldforInvestmentStudentLoanPortfoliobyProgramDetails</Role>
      <ShortName>Loans Held for Investment - Student Loan Portfolio by Program (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9954490 - Disclosure - Loans Held for Investment - Student Loan Portfolio Average Balances (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/LoansHeldforInvestmentStudentLoanPortfolioAverageBalancesDetails</Role>
      <ShortName>Loans Held for Investment - Student Loan Portfolio Average Balances (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9954491 - Disclosure - Loans Held for Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/LoansHeldforSaleDetails</Role>
      <ShortName>Loans Held for Sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/LoansHeldforSale</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9954492 - Disclosure - Allowance for Credit Losses - Allowance and Recorded Investments in Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesAllowanceandRecordedInvestmentsinLoansDetails</Role>
      <ShortName>Allowance for Credit Losses - Allowance and Recorded Investments in Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9954493 - Disclosure - Allowance for Credit Losses - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesNarrativeDetails</Role>
      <ShortName>Allowance for Credit Losses - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9954494 - Disclosure - Allowance for Credit Losses - Amortized Cost Basis of Financing Receivables with Loan Modifications (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesAmortizedCostBasisofFinancingReceivableswithLoanModificationsDetails</Role>
      <ShortName>Allowance for Credit Losses - Amortized Cost Basis of Financing Receivables with Loan Modifications (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9954495 - Disclosure - Allowance for Credit Losses - Amortized Cost Basis of Financing Receivables that Subsequently Defaulted (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesAmortizedCostBasisofFinancingReceivablesthatSubsequentlyDefaultedDetails</Role>
      <ShortName>Allowance for Credit Losses - Amortized Cost Basis of Financing Receivables that Subsequently Defaulted (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9954496 - Disclosure - Allowance for Credit Losses - Age Analysis of Pas Due Loans Delinquencies - Deferment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesAgeAnalysisofPasDueLoansDelinquenciesDefermentDetails</Role>
      <ShortName>Allowance for Credit Losses - Age Analysis of Pas Due Loans Delinquencies - Deferment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9954497 - Disclosure - Allowance for Credit Losses - Payment Status (Amortized Cost Basis) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesPaymentStatusAmortizedCostBasisDetails</Role>
      <ShortName>Allowance for Credit Losses - Payment Status (Amortized Cost Basis) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9954498 - Disclosure - Allowance for Credit Losses - Loan Portfolio Stratified by Key Credit Quality Indicators (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesLoanPortfolioStratifiedbyKeyCreditQualityIndicatorsDetails</Role>
      <ShortName>Allowance for Credit Losses - Loan Portfolio Stratified by Key Credit Quality Indicators (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9954499 - Disclosure - Allowance for Credit Losses - Age Analysis of Past Due Loans Delinquencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesAgeAnalysisofPastDueLoansDelinquenciesDetails</Role>
      <ShortName>Allowance for Credit Losses - Age Analysis of Past Due Loans Delinquencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9954500 - Disclosure - Allowance for Credit Losses - Accrued Interest Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/AllowanceforCreditLossesAccruedInterestReceivableDetails</Role>
      <ShortName>Allowance for Credit Losses - Accrued Interest Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9954501 - Disclosure - Unfunded Loan Commitments - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/UnfundedLoanCommitmentsNarrativeDetails</Role>
      <ShortName>Unfunded Loan Commitments - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9954502 - Disclosure - Unfunded Loan Commitments - Schedule of Allowance for Credit Losses and Recorded Investments in Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/UnfundedLoanCommitmentsScheduleofAllowanceforCreditLossesandRecordedInvestmentsinLoansDetails</Role>
      <ShortName>Unfunded Loan Commitments - Schedule of Allowance for Credit Losses and Recorded Investments in Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>9954503 - Disclosure - Goodwill and Acquired Intangible Assets - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/GoodwillandAcquiredIntangibleAssetsNarrativeDetails</Role>
      <ShortName>Goodwill and Acquired Intangible Assets - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>9954504 - Disclosure - Goodwill and Acquired Intangible Assets - Schedule of Acquired Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/GoodwillandAcquiredIntangibleAssetsScheduleofAcquiredIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Acquired Intangible Assets - Schedule of Acquired Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>9954505 - Disclosure - Deposits - Summary of Total Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DepositsSummaryofTotalDepositsDetails</Role>
      <ShortName>Deposits - Summary of Total Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>9954506 - Disclosure - Deposits - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DepositsNarrativeDetails</Role>
      <ShortName>Deposits - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>9954507 - Disclosure - Deposits - Interest Bearing Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DepositsInterestBearingDepositsDetails</Role>
      <ShortName>Deposits - Interest Bearing Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>9954508 - Disclosure - Deposits - Schedule of Remaining Maturities of Certificates of Deposit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DepositsScheduleofRemainingMaturitiesofCertificatesofDepositDetails</Role>
      <ShortName>Deposits - Schedule of Remaining Maturities of Certificates of Deposit (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>9954509 - Disclosure - Borrowings - Company Borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/BorrowingsCompanyBorrowingsDetails</Role>
      <ShortName>Borrowings - Company Borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>9954510 - Disclosure - Borrowings - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/BorrowingsNarrativeDetails</Role>
      <ShortName>Borrowings - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>9954511 - Disclosure - Borrowings - Secured Financing (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/BorrowingsSecuredFinancingDetails</Role>
      <ShortName>Borrowings - Secured Financing (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>9954512 - Disclosure - Borrowings - Financing VIEs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/BorrowingsFinancingVIEsDetails</Role>
      <ShortName>Borrowings - Financing VIEs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>9954513 - Disclosure - Borrowings - Summary of Exposure Related To Unconsolidated VIEs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/BorrowingsSummaryofExposureRelatedToUnconsolidatedVIEsDetails</Role>
      <ShortName>Borrowings - Summary of Exposure Related To Unconsolidated VIEs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>9954514 - Disclosure - Derivative Financial Instruments - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstrumentsNarrativeDetails</Role>
      <ShortName>Derivative Financial Instruments - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>9954515 - Disclosure - Derivative Financial Instruments - Impact of Derivatives on Consolidated Balance Sheet (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstrumentsImpactofDerivativesonConsolidatedBalanceSheetDetails</Role>
      <ShortName>Derivative Financial Instruments - Impact of Derivatives on Consolidated Balance Sheet (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>9954516 - Disclosure - Derivative Financial Instruments - Offsetting Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstrumentsOffsettingAssetsandLiabilitiesDetails</Role>
      <ShortName>Derivative Financial Instruments - Offsetting Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>9954517 - Disclosure - Derivative Financial Instruments - Notional Values (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstrumentsNotionalValuesDetails</Role>
      <ShortName>Derivative Financial Instruments - Notional Values (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>9954518 - Disclosure - Derivative Financial Instruments - Schedule of Hedged Items Recorded in Statement of Financial Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstrumentsScheduleofHedgedItemsRecordedinStatementofFinancialPositionDetails</Role>
      <ShortName>Derivative Financial Instruments - Schedule of Hedged Items Recorded in Statement of Financial Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>9954519 - Disclosure - Derivative Financial Instruments - Impact of Derivatives on Consolidated Statements of Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstrumentsImpactofDerivativesonConsolidatedStatementsofIncomeDetails</Role>
      <ShortName>Derivative Financial Instruments - Impact of Derivatives on Consolidated Statements of Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>9954520 - Disclosure - Derivative Financial Instruments - Impact of Derivatives on Consolidated Statement of Changes in Stockholders' Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/DerivativeFinancialInstrumentsImpactofDerivativesonConsolidatedStatementofChangesinStockholdersEquityDetails</Role>
      <ShortName>Derivative Financial Instruments - Impact of Derivatives on Consolidated Statement of Changes in Stockholders' Equity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>9954521 - Disclosure - Stockholders' Equity - Common Stock Repurchased (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/StockholdersEquityCommonStockRepurchasedDetails</Role>
      <ShortName>Stockholders' Equity - Common Stock Repurchased (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>9954522 - Disclosure - Stockholders' Equity - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/StockholdersEquityNarrativeDetails</Role>
      <ShortName>Stockholders' Equity - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>9954523 - Disclosure - Earnings (Loss) per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/EarningsLossperCommonShareDetails</Role>
      <ShortName>Earnings (Loss) per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/EarningsLossperCommonShareTables</ParentRole>
      <Position>79</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>9954524 - Disclosure - Fair Value Measurements - Valuation of Financial Instruments That are Marked-to-Market on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/FairValueMeasurementsValuationofFinancialInstrumentsThatareMarkedtoMarketonRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements - Valuation of Financial Instruments That are Marked-to-Market on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>9954525 - Disclosure - Fair Value Measurements - Fair Value Measurement Inputs and Valuation Techniques (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/FairValueMeasurementsFairValueMeasurementInputsandValuationTechniquesDetails</Role>
      <ShortName>Fair Value Measurements - Fair Value Measurement Inputs and Valuation Techniques (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>9954526 - Disclosure - Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/FairValueMeasurementsFairValuesofFinancialAssetsandLiabilitiesIncludingDerivativeFinancialInstrumentsDetails</Role>
      <ShortName>Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>9954527 - Disclosure - Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/FairValueMeasurementsFairValuesofFinancialAssetsandLiabilitiesIncludingDerivativeFinancialInstrumentsDetails_1</Role>
      <ShortName>Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>9954528 - Disclosure - Regulatory Capital - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/RegulatoryCapitalNarrativeDetails</Role>
      <ShortName>Regulatory Capital - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>9954529 - Disclosure - Regulatory Capital - Adjusted Transition Amounts (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/RegulatoryCapitalAdjustedTransitionAmountsDetails</Role>
      <ShortName>Regulatory Capital - Adjusted Transition Amounts (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>9954530 - Disclosure - Regulatory Capital - U.S. Basel III Regulatory Requirements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/RegulatoryCapitalUSBaselIIIRegulatoryRequirementsDetails</Role>
      <ShortName>Regulatory Capital - U.S. Basel III Regulatory Requirements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>9954531 - Disclosure - Commitments, Contingencies and Guarantees (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/CommitmentsContingenciesandGuaranteesDetails</Role>
      <ShortName>Commitments, Contingencies and Guarantees (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/CommitmentsContingenciesandGuarantees</ParentRole>
      <Position>87</Position>
    </Report>
    <Report instance="slm-20240930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>9954532 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.salliemae.com/role/SubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.salliemae.com/role/SubsequentEvent</ParentRole>
      <Position>88</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" isDefinitelyFs="true" isUsgaap="true" original="slm-20240930.htm">slm-20240930.htm</File>
    <File>slm-20240930.xsd</File>
    <File>slm-20240930_cal.xml</File>
    <File>slm-20240930_def.xml</File>
    <File>slm-20240930_lab.xml</File>
    <File>slm-20240930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="2">http://fasb.org/srt/2024</BaseTaxonomy>
    <BaseTaxonomy items="1945">http://fasb.org/us-gaap/2024</BaseTaxonomy>
    <BaseTaxonomy items="32">http://xbrl.sec.gov/dei/2024</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2024</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
