<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.4</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>1462</ContextCount>
  <ElementCount>850</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>222</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>10</UnitCount>
  <MyReports>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>0000002 - Document - Audit Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/AuditInformation</Role>
      <ShortName>Audit Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952151 - Statement - CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CONSOLIDATEDSTATEMENTSOFINCOME</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952152 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952153 - Statement - CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952154 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CONSOLIDATEDBALANCESHEETSParenthetical</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952155 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952156 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITYParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952157 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952158 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952159 - Disclosure - Business Combinations and Discontinued Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationsandDiscontinuedOperations</Role>
      <ShortName>Business Combinations and Discontinued Operations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952160 - Disclosure - Investment Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/InvestmentSecurities</Role>
      <ShortName>Investment Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - Loans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/Loans</Role>
      <ShortName>Loans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/AllowanceforCreditLossesandReserveforUnfundedLendingCommitments</Role>
      <ShortName>Allowance for Credit Losses and Reserve for Unfunded Lending Commitments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - Variable Interest Entities and Securitizations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/VariableInterestEntitiesandSecuritizations</Role>
      <ShortName>Variable Interest Entities and Securitizations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - Goodwill and Other Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/GoodwillandOtherIntangibleAssets</Role>
      <ShortName>Goodwill and Other Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - Premises, Equipment and Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/PremisesEquipmentandLeases</Role>
      <ShortName>Premises, Equipment and Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - Deposits and Borrowings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DepositsandBorrowings</Role>
      <ShortName>Deposits and Borrowings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - Derivative Instruments and Hedging Activities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivities</Role>
      <ShortName>Derivative Instruments and Hedging Activities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>9952168 - Disclosure - Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockholdersEquity</Role>
      <ShortName>Stockholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9952169 - Disclosure - Regulatory and Capital Adequacy</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/RegulatoryandCapitalAdequacy</Role>
      <ShortName>Regulatory and Capital Adequacy</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9952170 - Disclosure - Earnings Per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/EarningsPerCommonShare</Role>
      <ShortName>Earnings Per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>9952171 - Disclosure - Stock-Based Compensation Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockBasedCompensationPlans</Role>
      <ShortName>Stock-Based Compensation Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9952172 - Disclosure - Employee Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/EmployeeBenefitPlans</Role>
      <ShortName>Employee Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>9952173 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9952174 - Disclosure - Fair Value Measurement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurement</Role>
      <ShortName>Fair Value Measurement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9952175 - Disclosure - Business Segments and Revenue from Contracts with Customers</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessSegmentsandRevenuefromContractswithCustomers</Role>
      <ShortName>Business Segments and Revenue from Contracts with Customers</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9952176 - Disclosure - Commitments, Contingencies, Guarantees and Others</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CommitmentsContingenciesGuaranteesandOthers</Role>
      <ShortName>Commitments, Contingencies, Guarantees and Others</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9952177 - Disclosure - Capital One Financial Corporation (Parent Company Only)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnly</Role>
      <ShortName>Capital One Financial Corporation (Parent Company Only)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9952178 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/RelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9952179 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.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>32</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>995447 - Disclosure - Insider Trading Policies and Procedures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingPoliciesProc</Role>
      <ShortName>Insider Trading Policies and Procedures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>995550 - Disclosure - Cybersecurity Risk Management and Strategy Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/cyd/role/CybersecurityRiskManagementAndStrategyDisclosure</Role>
      <ShortName>Cybersecurity Risk Management and Strategy Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9955511 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9955512 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9955513 - Disclosure - Business Combination and Discontinued Operations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationandDiscontinuedOperationsTables</Role>
      <ShortName>Business Combination and Discontinued Operations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9955514 - Disclosure - Investment Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/InvestmentSecuritiesTables</Role>
      <ShortName>Investment Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/InvestmentSecurities</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9955515 - Disclosure - Loans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansTables</Role>
      <ShortName>Loans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/Loans</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9955516 - Disclosure - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/AllowanceforCreditLossesandReserveforUnfundedLendingCommitmentsTables</Role>
      <ShortName>Allowance for Credit Losses and Reserve for Unfunded Lending Commitments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/AllowanceforCreditLossesandReserveforUnfundedLendingCommitments</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9955517 - Disclosure - Variable Interest Entities and Securitizations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/VariableInterestEntitiesandSecuritizationsTables</Role>
      <ShortName>Variable Interest Entities and Securitizations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/VariableInterestEntitiesandSecuritizations</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9955518 - Disclosure - Goodwill and Other Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/GoodwillandOtherIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Other Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/GoodwillandOtherIntangibleAssets</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9955519 - Disclosure - Premises, Equipment and Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/PremisesEquipmentandLeasesTables</Role>
      <ShortName>Premises, Equipment and Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/PremisesEquipmentandLeases</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9955520 - Disclosure - Deposits and Borrowings (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DepositsandBorrowingsTables</Role>
      <ShortName>Deposits and Borrowings (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/DepositsandBorrowings</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9955521 - Disclosure - Derivative Instruments and Hedging Activities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivitiesTables</Role>
      <ShortName>Derivative Instruments and Hedging Activities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivities</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9955522 - Disclosure - Stockholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockholdersEquityTables</Role>
      <ShortName>Stockholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/StockholdersEquity</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9955523 - Disclosure - Regulatory and Capital Adequacy (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/RegulatoryandCapitalAdequacyTables</Role>
      <ShortName>Regulatory and Capital Adequacy (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/RegulatoryandCapitalAdequacy</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9955524 - Disclosure - Earnings Per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/EarningsPerCommonShareTables</Role>
      <ShortName>Earnings Per Common Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/EarningsPerCommonShare</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9955525 - Disclosure - Stock-Based Compensation Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockBasedCompensationPlansTables</Role>
      <ShortName>Stock-Based Compensation Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/StockBasedCompensationPlans</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9955526 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/IncomeTaxes</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9955527 - Disclosure - Fair Value Measurement (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurementTables</Role>
      <ShortName>Fair Value Measurement (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/FairValueMeasurement</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9955528 - Disclosure - Business Segments and Revenue from Contracts with Customers (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessSegmentsandRevenuefromContractswithCustomersTables</Role>
      <ShortName>Business Segments and Revenue from Contracts with Customers (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/BusinessSegmentsandRevenuefromContractswithCustomers</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9955529 - Disclosure - Commitments, Contingencies, Guarantees and Others (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CommitmentsContingenciesGuaranteesandOthersTables</Role>
      <ShortName>Commitments, Contingencies, Guarantees and Others (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/CommitmentsContingenciesGuaranteesandOthers</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9955530 - Disclosure - Capital One Financial Corporation (Parent Company Only) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnlyTables</Role>
      <ShortName>Capital One Financial Corporation (Parent Company Only) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnly</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9955531 - Disclosure - Summary of Significant Accounting Policies - Segments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPoliciesSegmentsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Segments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9955532 - Disclosure - Summary of Significant Accounting Policies - Voting Interest Entities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPoliciesVotingInterestEntitiesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Voting Interest Entities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9955533 - Disclosure - Summary of Significant Accounting Policies - Loans and Allowance for Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPoliciesLoansandAllowanceforCreditLossesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Loans and Allowance for Credit Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9955534 - Disclosure - Summary of Significant Accounting Policies - Useful Lives for Premises and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPoliciesUsefulLivesforPremisesandEquipmentDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Useful Lives for Premises and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>9955535 - Disclosure - Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPoliciesGoodwillandOtherIntangibleAssetsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>9955536 - Disclosure - Summary of Significant Accounting Policies - Revenue Recognition (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Revenue Recognition (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>9955537 - Disclosure - Business Combinations and Discontinued Operations - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationsandDiscontinuedOperationsAdditionalInformationDetails</Role>
      <ShortName>Business Combinations and Discontinued Operations - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>9955538 - Disclosure - Business Combinations and Discontinued Operations - Schedule of Preferred Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationsandDiscontinuedOperationsScheduleofPreferredStockDetails</Role>
      <ShortName>Business Combinations and Discontinued Operations - Schedule of Preferred Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>9955539 - Disclosure - Business Combinations and Discontinued Operations - Business Combination (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationsandDiscontinuedOperationsBusinessCombinationDetails</Role>
      <ShortName>Business Combinations and Discontinued Operations - Business Combination (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>9955540 - Disclosure - Business Combinations and Discontinued Operations - Investment Holdings, Other than Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationsandDiscontinuedOperationsInvestmentHoldingsOtherthanSecuritiesDetails</Role>
      <ShortName>Business Combinations and Discontinued Operations - Investment Holdings, Other than Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>9955541 - Disclosure - Business Combinations and Discontinued Operations - Schedule of Finite-Lived Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationsandDiscontinuedOperationsScheduleofFiniteLivedIntangibleAssetsDetails</Role>
      <ShortName>Business Combinations and Discontinued Operations - Schedule of Finite-Lived Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>9955542 - Disclosure - Business Combinations and Discontinued Operations - Deposit Liabilities, Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationsandDiscontinuedOperationsDepositLiabilitiesTypeDetails</Role>
      <ShortName>Business Combinations and Discontinued Operations - Deposit Liabilities, Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>9955543 - Disclosure - Business Combinations and Discontinued Operations - Schedule of Operating Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessCombinationsandDiscontinuedOperationsScheduleofOperatingIncomeDetails</Role>
      <ShortName>Business Combinations and Discontinued Operations - Schedule of Operating Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>9955544 - Disclosure - Investment Securities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/InvestmentSecuritiesAdditionalInformationDetails</Role>
      <ShortName>Investment Securities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>9955545 - Disclosure - Investment Securities - Investment Available for Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/InvestmentSecuritiesInvestmentAvailableforSaleDetails</Role>
      <ShortName>Investment Securities - Investment Available for Sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>9955546 - Disclosure - Investment Securities - Securities in Gross Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/InvestmentSecuritiesSecuritiesinGrossUnrealizedLossPositionDetails</Role>
      <ShortName>Investment Securities - Securities in Gross Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>9955547 - Disclosure - Investment Securities - Contractual Maturities and Weighted-Average Yields of Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/InvestmentSecuritiesContractualMaturitiesandWeightedAverageYieldsofSecuritiesDetails</Role>
      <ShortName>Investment Securities - Contractual Maturities and Weighted-Average Yields of Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>9955548 - Disclosure - Investment Securities - Realized Gains and Losses on Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/InvestmentSecuritiesRealizedGainsandLossesonSecuritiesDetails</Role>
      <ShortName>Investment Securities - Realized Gains and Losses on Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>9955549 - Disclosure - Loans - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansAdditionalInformationDetails</Role>
      <ShortName>Loans - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>9955550 - Disclosure - Loans - Loan Portfolio Composition and Aging Analysis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansLoanPortfolioCompositionandAgingAnalysisDetails</Role>
      <ShortName>Loans - Loan Portfolio Composition and Aging Analysis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>9955551 - Disclosure - Loans - 90+ Day Delinquent Loans Accruing Interest and Nonperforming Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/Loans90DayDelinquentLoansAccruingInterestandNonperformingLoansDetails</Role>
      <ShortName>Loans - 90+ Day Delinquent Loans Accruing Interest and Nonperforming Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>9955552 - Disclosure - Loans - Credit Card Delinquency Status (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansCreditCardDelinquencyStatusDetails</Role>
      <ShortName>Loans - Credit Card Delinquency Status (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>9955553 - Disclosure - Loans - Consumer Banking Portfolio by Credit Quality Indicator (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansConsumerBankingPortfoliobyCreditQualityIndicatorDetails</Role>
      <ShortName>Loans - Consumer Banking Portfolio by Credit Quality Indicator (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>9955554 - Disclosure - Loans - Commercial Banking: Risk Profile by Internal Risk Rating (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansCommercialBankingRiskProfilebyInternalRiskRatingDetails</Role>
      <ShortName>Loans - Commercial Banking: Risk Profile by Internal Risk Rating (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>9955555 - Disclosure - Loans - Financing Receivable, Modified - Modification to Borrowers (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansFinancingReceivableModifiedModificationtoBorrowersDetails</Role>
      <ShortName>Loans - Financing Receivable, Modified - Modification to Borrowers (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>9955556 - Disclosure - Loans - FDM Disclosure - Modification to Borrowers (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansFDMDisclosureModificationtoBorrowersDetails</Role>
      <ShortName>Loans - FDM Disclosure - Modification to Borrowers (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>9955557 - Disclosure - Loans - Schedule of Debtor Troubled Debt Restructuring, Subsequent Periods (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/LoansScheduleofDebtorTroubledDebtRestructuringSubsequentPeriodsDetails</Role>
      <ShortName>Loans - Schedule of Debtor Troubled Debt Restructuring, Subsequent Periods (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>9955558 - Disclosure - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/AllowanceforCreditLossesandReserveforUnfundedLendingCommitmentsAdditionalInformationDetails</Role>
      <ShortName>Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>9955559 - Disclosure - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/AllowanceforCreditLossesandReserveforUnfundedLendingCommitmentsAllowanceforCreditLossesandReserveforUnfundedLendingCommitmentsActivityDetails</Role>
      <ShortName>Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>9955560 - Disclosure - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Charge-Offs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/AllowanceforCreditLossesandReserveforUnfundedLendingCommitmentsChargeOffsDetails</Role>
      <ShortName>Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Charge-Offs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/AllowanceforCreditLossesandReserveforUnfundedLendingCommitmentsTables</ParentRole>
      <Position>84</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>9955561 - Disclosure - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Summary of Loss Sharing Arrangements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/AllowanceforCreditLossesandReserveforUnfundedLendingCommitmentsSummaryofLossSharingArrangementsDetails</Role>
      <ShortName>Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Summary of Loss Sharing Arrangements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>9955562 - Disclosure - Variable Interest Entities and Securitizations - Carrying Amount of Consolidated and Unconsolidated VIEs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/VariableInterestEntitiesandSecuritizationsCarryingAmountofConsolidatedandUnconsolidatedVIEsDetails</Role>
      <ShortName>Variable Interest Entities and Securitizations - Carrying Amount of Consolidated and Unconsolidated VIEs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>9955563 - Disclosure - Variable Interest Entities and Securitizations - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/VariableInterestEntitiesandSecuritizationsAdditionalInformationDetails</Role>
      <ShortName>Variable Interest Entities and Securitizations - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>9955564 - Disclosure - Goodwill and Other Intangible Assets - Components (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/GoodwillandOtherIntangibleAssetsComponentsDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Components (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>9955565 - Disclosure - Goodwill and Other Intangible Assets - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/GoodwillandOtherIntangibleAssetsAdditionalInformationDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>9955566 - Disclosure - Goodwill and Other Intangible Assets - Actual and Estimated Future Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/GoodwillandOtherIntangibleAssetsActualandEstimatedFutureAmortizationExpenseDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Actual and Estimated Future Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>9955567 - Disclosure - Goodwill and Other Intangible Assets - Goodwill Business Segments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/GoodwillandOtherIntangibleAssetsGoodwillBusinessSegmentsDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Goodwill Business Segments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>9955568 - Disclosure - Premises, Equipment and Leases - Components of Premises and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/PremisesEquipmentandLeasesComponentsofPremisesandEquipmentDetails</Role>
      <ShortName>Premises, Equipment and Leases - Components of Premises and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>9955569 - Disclosure - Premises, Equipment and Leases - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/PremisesEquipmentandLeasesAdditionalInformationDetails</Role>
      <ShortName>Premises, Equipment and Leases - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>9955570 - Disclosure - Premises, Equipment and Leases - Operating Lease Portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/PremisesEquipmentandLeasesOperatingLeasePortfolioDetails</Role>
      <ShortName>Premises, Equipment and Leases - Operating Lease Portfolio (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>9955571 - Disclosure - Premises, Equipment and Leases - Maturities of Operating Leases and Reconciliation to Lease Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/PremisesEquipmentandLeasesMaturitiesofOperatingLeasesandReconciliationtoLeaseLiabilitiesDetails</Role>
      <ShortName>Premises, Equipment and Leases - Maturities of Operating Leases and Reconciliation to Lease Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>9955572 - Disclosure - Deposits and Borrowings - Deposits and Short-term Borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DepositsandBorrowingsDepositsandShorttermBorrowingsDetails</Role>
      <ShortName>Deposits and Borrowings - Deposits and Short-term Borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>9955573 - Disclosure - Deposits and Borrowings - Long-Term Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DepositsandBorrowingsLongTermDebtDetails</Role>
      <ShortName>Deposits and Borrowings - Long-Term Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>9955574 - Disclosure - Deposits and Borrowings - Maturity Profile of Borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DepositsandBorrowingsMaturityProfileofBorrowingsDetails</Role>
      <ShortName>Deposits and Borrowings - Maturity Profile of Borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>9955575 - Disclosure - Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivitiesDerivativeAssetsandLiabilitiesatFairValueDetails</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>9955576 - Disclosure - Derivative Instruments and Hedging Activities - Hedged Items in Fair Value Hedging Relationship (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivitiesHedgedItemsinFairValueHedgingRelationshipDetails</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Hedged Items in Fair Value Hedging Relationship (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>9955577 - Disclosure - Derivative Instruments and Hedging Activities - Offsetting Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivitiesOffsettingAssetsDetails</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Offsetting Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>9955578 - Disclosure - Derivative Instruments and Hedging Activities - Offsetting Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivitiesOffsettingLiabilitiesDetails</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Offsetting Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>102</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>9955579 - Disclosure - Derivative Instruments and Hedging Activities - Effects of Fair Value and Cash Flow Hedge Accounting (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivitiesEffectsofFairValueandCashFlowHedgeAccountingDetails</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Effects of Fair Value and Cash Flow Hedge Accounting (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>9955580 - Disclosure - Derivative Instruments and Hedging Activities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivitiesAdditionalInformationDetails</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>104</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>9955581 - Disclosure - Derivative Instruments and Hedging Activities - Gains Losses on Freestanding Derivatives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/DerivativeInstrumentsandHedgingActivitiesGainsLossesonFreestandingDerivativesDetails</Role>
      <ShortName>Derivative Instruments and Hedging Activities - Gains Losses on Freestanding Derivatives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>105</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>9955582 - Disclosure - Stockholders' Equity - Preferred Stock Outstanding (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockholdersEquityPreferredStockOutstandingDetails</Role>
      <ShortName>Stockholders' Equity - Preferred Stock Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>106</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R107.htm</HtmlFileName>
      <LongName>9955583 - Disclosure - Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockholdersEquityAccumulatedOtherComprehensiveIncomeLossDetails</Role>
      <ShortName>Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>107</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R108.htm</HtmlFileName>
      <LongName>9955584 - Disclosure - Stockholders' Equity - Reclassifications from AOCI (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockholdersEquityReclassificationsfromAOCIDetails</Role>
      <ShortName>Stockholders' Equity - Reclassifications from AOCI (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>108</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>9955585 - Disclosure - Stockholders' Equity - Other Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockholdersEquityOtherComprehensiveIncomeDetails</Role>
      <ShortName>Stockholders' Equity - Other Comprehensive Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>109</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>9955586 - Disclosure - Regulatory and Capital Adequacy - Capital Ratios Under Basel III (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/RegulatoryandCapitalAdequacyCapitalRatiosUnderBaselIIIDetails</Role>
      <ShortName>Regulatory and Capital Adequacy - Capital Ratios Under Basel III (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>110</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R111.htm</HtmlFileName>
      <LongName>9955587 - Disclosure - Regulatory and Capital Adequacy - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/RegulatoryandCapitalAdequacyAdditionalInformationDetails</Role>
      <ShortName>Regulatory and Capital Adequacy - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>111</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R112.htm</HtmlFileName>
      <LongName>9955588 - Disclosure - Earnings Per Common Share - Computation of Basic and Diluted Earnings Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/EarningsPerCommonShareComputationofBasicandDilutedEarningsPerCommonShareDetails</Role>
      <ShortName>Earnings Per Common Share - Computation of Basic and Diluted Earnings Per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>112</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R113.htm</HtmlFileName>
      <LongName>9955589 - Disclosure - Stock-Based Compensation Plans - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockBasedCompensationPlansAdditionalInformationDetails</Role>
      <ShortName>Stock-Based Compensation Plans - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>113</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R114.htm</HtmlFileName>
      <LongName>9955590 - Disclosure - Stock-Based Compensation Plans - Summary of Restricted Stock Units and Performance Share Units (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/StockBasedCompensationPlansSummaryofRestrictedStockUnitsandPerformanceShareUnitsDetails</Role>
      <ShortName>Stock-Based Compensation Plans - Summary of Restricted Stock Units and Performance Share Units (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>114</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>9955591 - Disclosure - Employee Benefit Plans - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/EmployeeBenefitPlansAdditionalInformationDetails</Role>
      <ShortName>Employee Benefit Plans - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>115</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>9955592 - Disclosure - Income Taxes - Significant Components of Provision for Income Taxes Attributable to Continuing Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/IncomeTaxesSignificantComponentsofProvisionforIncomeTaxesAttributabletoContinuingOperationsDetails</Role>
      <ShortName>Income Taxes - Significant Components of Provision for Income Taxes Attributable to Continuing Operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>116</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R117.htm</HtmlFileName>
      <LongName>9955593 - Disclosure - Income Taxes - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/IncomeTaxesAdditionalInformationDetails</Role>
      <ShortName>Income Taxes - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>117</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R118.htm</HtmlFileName>
      <LongName>9955594 - Disclosure - Income Taxes - Effective Income Tax Rate (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/IncomeTaxesEffectiveIncomeTaxRateDetails</Role>
      <ShortName>Income Taxes - Effective Income Tax Rate (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>118</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R119.htm</HtmlFileName>
      <LongName>9955595 - Disclosure - Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/IncomeTaxesSignificantComponentsofDeferredTaxAssetsandLiabilitiesDetails</Role>
      <ShortName>Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>119</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R120.htm</HtmlFileName>
      <LongName>9955596 - Disclosure - Income Taxes - Reconciliation of Change in Unrecognized Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/IncomeTaxesReconciliationofChangeinUnrecognizedTaxBenefitsDetails</Role>
      <ShortName>Income Taxes - Reconciliation of Change in Unrecognized Tax Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>120</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R121.htm</HtmlFileName>
      <LongName>9955597 - Disclosure - Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurementAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>121</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R122.htm</HtmlFileName>
      <LongName>9955598 - Disclosure - Fair Value Measurement - Level 3 Recurring Fair Value Rollforward (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurementLevel3RecurringFairValueRollforwardDetails</Role>
      <ShortName>Fair Value Measurement - Level 3 Recurring Fair Value Rollforward (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>122</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R123.htm</HtmlFileName>
      <LongName>9955599 - Disclosure - Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurementQuantitativeInformationaboutLevel3FairValueMeasurementsDetails</Role>
      <ShortName>Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>123</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R124.htm</HtmlFileName>
      <LongName>9955600 - Disclosure - Fair Value Measurement - Nonrecurring Fair Value Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurementNonrecurringFairValueMeasurementsDetails</Role>
      <ShortName>Fair Value Measurement - Nonrecurring Fair Value Measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>124</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R125.htm</HtmlFileName>
      <LongName>9955601 - Disclosure - Fair Value Measurement - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurementAdditionalInformationDetails</Role>
      <ShortName>Fair Value Measurement - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>125</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R126.htm</HtmlFileName>
      <LongName>9955602 - Disclosure - Fair Value Measurement - Nonrecurring Fair Value Measurements Included in Earnings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurementNonrecurringFairValueMeasurementsIncludedinEarningsDetails</Role>
      <ShortName>Fair Value Measurement - Nonrecurring Fair Value Measurements Included in Earnings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>126</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R127.htm</HtmlFileName>
      <LongName>9955603 - Disclosure - Fair Value Measurement - Fair Value of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/FairValueMeasurementFairValueofFinancialInstrumentsDetails</Role>
      <ShortName>Fair Value Measurement - Fair Value of Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>127</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R128.htm</HtmlFileName>
      <LongName>9955604 - Disclosure - Business Segments and Revenue from Contracts with Customers - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessSegmentsandRevenuefromContractswithCustomersAdditionalInformationDetails</Role>
      <ShortName>Business Segments and Revenue from Contracts with Customers - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>128</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R129.htm</HtmlFileName>
      <LongName>9955605 - Disclosure - Business Segments and Revenue from Contracts with Customers - Segment Results and Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessSegmentsandRevenuefromContractswithCustomersSegmentResultsandReconciliationDetails</Role>
      <ShortName>Business Segments and Revenue from Contracts with Customers - Segment Results and Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>129</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R130.htm</HtmlFileName>
      <LongName>9955606 - Disclosure - Business Segments and Revenue from Contracts with Customers - Revenue from Contracts with Customers (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/BusinessSegmentsandRevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails</Role>
      <ShortName>Business Segments and Revenue from Contracts with Customers - Revenue from Contracts with Customers (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>130</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R131.htm</HtmlFileName>
      <LongName>9955607 - Disclosure - Commitments, Contingencies, Guarantees and Others - Unfunded Lending Commitments: Contractual Amount and Carrying Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CommitmentsContingenciesGuaranteesandOthersUnfundedLendingCommitmentsContractualAmountandCarryingValueDetails</Role>
      <ShortName>Commitments, Contingencies, Guarantees and Others - Unfunded Lending Commitments: Contractual Amount and Carrying Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>131</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R132.htm</HtmlFileName>
      <LongName>9955608 - Disclosure - Commitments, Contingencies, Guarantees and Others - Loss Sharing Agreements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CommitmentsContingenciesGuaranteesandOthersLossSharingAgreementsDetails</Role>
      <ShortName>Commitments, Contingencies, Guarantees and Others - Loss Sharing Agreements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>132</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R133.htm</HtmlFileName>
      <LongName>9955609 - Disclosure - Commitments, Contingencies, Guarantees and Others - Litigation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CommitmentsContingenciesGuaranteesandOthersLitigationDetails</Role>
      <ShortName>Commitments, Contingencies, Guarantees and Others - Litigation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>133</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R134.htm</HtmlFileName>
      <LongName>9955610 - Disclosure - Commitments, Contingencies, Guarantees and Others - Other Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CommitmentsContingenciesGuaranteesandOthersOtherContingenciesDetails</Role>
      <ShortName>Commitments, Contingencies, Guarantees and Others - Other Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>134</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R135.htm</HtmlFileName>
      <LongName>9955611 - Disclosure - Capital One Financial Corporation (Parent Company Only) - Statements of Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnlyStatementsofIncomeDetails</Role>
      <ShortName>Capital One Financial Corporation (Parent Company Only) - Statements of Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnlyTables</ParentRole>
      <Position>135</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R136.htm</HtmlFileName>
      <LongName>9955612 - Disclosure - Capital One Financial Corporation (Parent Company Only) - Balance Sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnlyBalanceSheetsDetails</Role>
      <ShortName>Capital One Financial Corporation (Parent Company Only) - Balance Sheets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnlyTables</ParentRole>
      <Position>136</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R137.htm</HtmlFileName>
      <LongName>9955613 - Disclosure - Capital One Financial Corporation (Parent Company Only) - Statements of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnlyStatementsofCashFlowsDetails</Role>
      <ShortName>Capital One Financial Corporation (Parent Company Only) - Statements of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/CapitalOneFinancialCorporationParentCompanyOnlyTables</ParentRole>
      <Position>137</Position>
    </Report>
    <Report instance="cof-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R138.htm</HtmlFileName>
      <LongName>9955614 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.capitalone.com/role/SubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.capitalone.com/role/SubsequentEvents</ParentRole>
      <Position>138</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-K" isDefinitelyFs="true" isUsgaap="true" original="cof-20251231.htm">cof-20251231.htm</File>
    <File>cof-20251231.xsd</File>
    <File>cof-20251231_cal.xml</File>
    <File>cof-20251231_def.xml</File>
    <File>cof-20251231_lab.xml</File>
    <File>cof-20251231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>cof-20251231_g1.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="3">http://fasb.org/srt/2025</BaseTaxonomy>
    <BaseTaxonomy items="4199">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="15">http://xbrl.sec.gov/cyd/2025</BaseTaxonomy>
    <BaseTaxonomy items="60">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="36">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
