<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.10.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>1611</ContextCount>
  <ElementCount>496</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>143</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/DocumentAndEntityInformation</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Consolidated Statements of Earnings (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ConsolidatedStatementsOfEarningsUnaudited</Role>
      <ShortName>Consolidated Statements of Earnings (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002000 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1003000 - Statement - Consolidated Balance Sheets (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ConsolidatedBalanceSheetsUnaudited</Role>
      <ShortName>Consolidated Balance Sheets (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003501 - Statement - Consolidated Balance Sheets (Parenthetical) (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ConsolidatedBalanceSheetsParentheticalUnaudited</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical) (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004000 - Statement - Consolidated Statements of Changes in Equity (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ConsolidatedStatementsOfChangesInEquityUnaudited</Role>
      <ShortName>Consolidated Statements of Changes in Equity (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1005000 - Statement - Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ConsolidatedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>Consolidated Statements of Cash Flows (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/SignificantAccountingPolicies</Role>
      <ShortName>Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/Securities</Role>
      <ShortName>Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Derivatives</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/Derivatives</Role>
      <ShortName>Derivatives</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - Loans and Allowances for Credit Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/LoansAndAllowancesForCreditLosses</Role>
      <ShortName>Loans and Allowances for Credit Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2115100 - Disclosure - Acquisition Acquisition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/AcquisitionAcquisition</Role>
      <ShortName>Acquisition Acquisition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2116100 - Disclosure - Mortgage Banking Activities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/MortgageBankingActivities</Role>
      <ShortName>Mortgage Banking Activities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2117100 - Disclosure - Commitments and Contingent Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/CommitmentsAndContingentLiabilities</Role>
      <ShortName>Commitments and Contingent Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2118100 - Disclosure - Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ShareholdersEquity</Role>
      <ShortName>Shareholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2119100 - Disclosure - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/EarningsPerShare</Role>
      <ShortName>Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2120100 - Disclosure - Reportable Segments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ReportableSegments</Role>
      <ShortName>Reportable Segments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2122100 - Disclosure - Fees and Commissions Revenue Fees and Commissions Revenue</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FeesAndCommissionsRevenueFeesAndCommissionsRevenue</Role>
      <ShortName>Fees and Commissions Revenue Fees and Commissions Revenue</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2123100 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2124100 - Disclosure - Federal and State Income Taxes Federal and State Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FederalAndStateIncomeTaxesFederalAndStateIncomeTaxes</Role>
      <ShortName>Federal and State Income Taxes Federal and State Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2125100 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2201201 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/SignificantAccountingPoliciesPolicies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.bokf.com/role/SignificantAccountingPolicies</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2302301 - Disclosure - Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/SecuritiesTables</Role>
      <ShortName>Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/Securities</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2303301 - Disclosure - Derivatives (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/DerivativesTables</Role>
      <ShortName>Derivatives (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/Derivatives</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2304301 - Disclosure - Loans and Allowances for Credit Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/LoansAndAllowancesForCreditLossesTables</Role>
      <ShortName>Loans and Allowances for Credit Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/LoansAndAllowancesForCreditLosses</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2316301 - Disclosure - Mortgage Banking Activities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/MortgageBankingActivitiesTables</Role>
      <ShortName>Mortgage Banking Activities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/MortgageBankingActivities</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2317301 - Disclosure - Commitments and Contingent Liabilities Commitments and Contingent Liabilities - Variable Interest Entities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/CommitmentsAndContingentLiabilitiesCommitmentsAndContingentLiabilitiesVariableInterestEntitiesTables</Role>
      <ShortName>Commitments and Contingent Liabilities Commitments and Contingent Liabilities - Variable Interest Entities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2318301 - Disclosure - Shareholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ShareholdersEquityTables</Role>
      <ShortName>Shareholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/ShareholdersEquity</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2319301 - Disclosure - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/EarningsPerShareTables</Role>
      <ShortName>Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/EarningsPerShare</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2320301 - Disclosure - Reportable Segments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ReportableSegmentsTables</Role>
      <ShortName>Reportable Segments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/ReportableSegments</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2322301 - Disclosure - Fees and Commissions Revenue Fees and Commissions Rvenue (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FeesAndCommissionsRevenueFeesAndCommissionsRvenueTables</Role>
      <ShortName>Fees and Commissions Revenue Fees and Commissions Rvenue (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/FeesAndCommissionsRevenueFeesAndCommissionsRevenue</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2323301 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/FairValueMeasurements</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2324301 - Disclosure - Federal and State Income Taxes Federal and State Income Taes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FederalAndStateIncomeTaxesFederalAndStateIncomeTaesTables</Role>
      <ShortName>Federal and State Income Taxes Federal and State Income Taes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.bokf.com/role/FederalAndStateIncomeTaxesFederalAndStateIncomeTaxes</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2401402 - Disclosure - Significant Accounting Policies Loans and Allowance for Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/SignificantAccountingPoliciesLoansAndAllowanceForCreditLossesDetails</Role>
      <ShortName>Significant Accounting Policies Loans and Allowance for Credit Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2401403 - Disclosure - Significant Accounting Policies Newly Adopted and Pending Accounting Pronouncements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/SignificantAccountingPoliciesNewlyAdoptedAndPendingAccountingPronouncementsDetails</Role>
      <ShortName>Significant Accounting Policies Newly Adopted and Pending Accounting Pronouncements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2402402 - Disclosure - Trading Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/TradingSecuritiesDetails</Role>
      <ShortName>Trading Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2402403 - Disclosure - Investment (Held-to-Maturity) Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/InvestmentHeldToMaturitySecuritiesDetails</Role>
      <ShortName>Investment (Held-to-Maturity) Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2402404 - Disclosure - Available for Sale Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/AvailableForSaleSecuritiesDetails</Role>
      <ShortName>Available for Sale Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2402405 - Disclosure - Securities Fair Value Option Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/SecuritiesFairValueOptionSecuritiesDetails</Role>
      <ShortName>Securities Fair Value Option Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2403402 - Disclosure - Derivatives, Fair Value of Derivatives Contracts (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/DerivativesFairValueOfDerivativesContractsDetails</Role>
      <ShortName>Derivatives, Fair Value of Derivatives Contracts (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2403403 - Disclosure - Derivatives, Derivatives Instruments Gain (Loss) in Income Statement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/DerivativesDerivativesInstrumentsGainLossInIncomeStatementDetails</Role>
      <ShortName>Derivatives, Derivatives Instruments Gain (Loss) in Income Statement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2404402 - Disclosure - Loans and Allowance for Credit Losses, Loans by Portfolio Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/LoansAndAllowanceForCreditLossesLoansByPortfolioTypeDetails</Role>
      <ShortName>Loans and Allowance for Credit Losses, Loans by Portfolio Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2404403 - Disclosure - Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/LoansAndAllowancesForCreditLossesActivityInAllowanceForCreditLossesDetails</Role>
      <ShortName>Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2404404 - Disclosure - Loans and Allowances for Credit Losses, Credit Quality Indicators (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/LoansAndAllowancesForCreditLossesCreditQualityIndicatorsDetails</Role>
      <ShortName>Loans and Allowances for Credit Losses, Credit Quality Indicators (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2404405 - Disclosure - Loans and Allowance for Credit Losses, Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/LoansAndAllowanceForCreditLossesImpairedLoansDetails</Role>
      <ShortName>Loans and Allowance for Credit Losses, Impaired Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2404406 - Disclosure - Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/LoansAndAllowancesForCreditLossesTroubledDebtRestructuringsDetails</Role>
      <ShortName>Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2404407 - Disclosure - Loans and Allowances for Credit Losses, By Aging Category (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/LoansAndAllowancesForCreditLossesByAgingCategoryDetails</Role>
      <ShortName>Loans and Allowances for Credit Losses, By Aging Category (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2415402 - Disclosure - Acquisition Acquisitions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/AcquisitionAcquisitionsDetails</Role>
      <ShortName>Acquisition Acquisitions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.bokf.com/role/AcquisitionAcquisition</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2416402 - Disclosure - Mortgage Banking Activities, Components of Loans Held For Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/MortgageBankingActivitiesComponentsOfLoansHeldForSaleDetails</Role>
      <ShortName>Mortgage Banking Activities, Components of Loans Held For Sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2416403 - Disclosure - Mortgage Banking Activities Mortgage Banking Activities, Mortgage Banking Revenue (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/MortgageBankingActivitiesMortgageBankingActivitiesMortgageBankingRevenueDetails</Role>
      <ShortName>Mortgage Banking Activities Mortgage Banking Activities, Mortgage Banking Revenue (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2416404 - Disclosure - Mortgage Banking Activities, Mortgage Servicing Rights (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/MortgageBankingActivitiesMortgageServicingRightsDetails</Role>
      <ShortName>Mortgage Banking Activities, Mortgage Servicing Rights (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2416405 - Disclosure - Mortgage Banking Activities Mortgage Banking Activities, Loans Serviced for Others (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/MortgageBankingActivitiesMortgageBankingActivitiesLoansServicedForOthersDetails</Role>
      <ShortName>Mortgage Banking Activities Mortgage Banking Activities, Loans Serviced for Others (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2417402 - Disclosure - Commitments and Contingent Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/CommitmentsAndContingentLiabilitiesDetails</Role>
      <ShortName>Commitments and Contingent Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.bokf.com/role/CommitmentsAndContingentLiabilitiesCommitmentsAndContingentLiabilitiesVariableInterestEntitiesTables</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2417403 - Disclosure - Commitments and Contingent Liabilities Variable Interest Entities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/CommitmentsAndContingentLiabilitiesVariableInterestEntitiesDetails</Role>
      <ShortName>Commitments and Contingent Liabilities Variable Interest Entities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2418402 - Disclosure - Shareholders' Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ShareholdersEquityDetails</Role>
      <ShortName>Shareholders' Equity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.bokf.com/role/ShareholdersEquityTables</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2419402 - Disclosure - Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/EarningsPerShareDetails</Role>
      <ShortName>Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.bokf.com/role/EarningsPerShareTables</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2420402 - Disclosure - Reportable Segments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/ReportableSegmentsDetails</Role>
      <ShortName>Reportable Segments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.bokf.com/role/ReportableSegmentsTables</ParentRole>
      <Position>57</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2422402 - Disclosure - Fees and Commissions Revenue Fees and Commissions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FeesAndCommissionsRevenueFeesAndCommissionsDetails</Role>
      <ShortName>Fees and Commissions Revenue Fees and Commissions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.bokf.com/role/FeesAndCommissionsRevenueFeesAndCommissionsRvenueTables</ParentRole>
      <Position>58</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2423402 - Disclosure - Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FairValueMeasurementsFairValueOfFinancialInstrumentsAsMeasuredOnRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2423403 - Disclosure - Fair Value Measurements, Measured On Recurring Basis Significant Unobservable Inputs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FairValueMeasurementsMeasuredOnRecurringBasisSignificantUnobservableInputsDetails</Role>
      <ShortName>Fair Value Measurements, Measured On Recurring Basis Significant Unobservable Inputs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2423404 - Disclosure - Fair Value Measurements Fair Value Measurements, Financial Instruments Measured On a Recurring Basis, Quantitative Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FairValueMeasurementsFairValueMeasurementsFinancialInstrumentsMeasuredOnRecurringBasisQuantitativeInformationDetails</Role>
      <ShortName>Fair Value Measurements Fair Value Measurements, Financial Instruments Measured On a Recurring Basis, Quantitative Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2423405 - Disclosure - Fair Value Measurements, Fair Value Measured On a Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FairValueMeasurementsFairValueMeasuredOnNonrecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements, Fair Value Measured On a Nonrecurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2423406 - Disclosure - Fair Value Measurements Fair Value Measurement, Measured On Non-Recurring Basis, Signfiicant Unobservable Inputs, Quantitative Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FairValueMeasurementsFairValueMeasurementMeasuredOnNonRecurringBasisSignfiicantUnobservableInputsQuantitativeInformationDetails</Role>
      <ShortName>Fair Value Measurements Fair Value Measurement, Measured On Non-Recurring Basis, Signfiicant Unobservable Inputs, Quantitative Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2423407 - Disclosure - Fair Value Measurements, Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FairValueMeasurementsFinancialInstrumentsDetails</Role>
      <ShortName>Fair Value Measurements, Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="a20180930bokf10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2424402 - Disclosure - Federal and State Income Taxes Federal and State Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.bokf.com/role/FederalAndStateIncomeTaxesFederalAndStateIncomeTaxesDetails</Role>
      <ShortName>Federal and State Income Taxes Federal and State Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.bokf.com/role/FederalAndStateIncomeTaxesFederalAndStateIncomeTaesTables</ParentRole>
      <Position>65</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" original="a20180930bokf10q.htm">a20180930bokf10q.htm</File>
    <File>a20180930bokfex311.htm</File>
    <File>a20180930bokfex312.htm</File>
    <File>a20180930bokfex32.htm</File>
    <File>bokf-20180630.xsd</File>
    <File>bokf-20180630_cal.xml</File>
    <File>bokf-20180630_def.xml</File>
    <File>bokf-20180630_lab.xml</File>
    <File>bokf-20180630_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/stpr/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/invest/2013-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2018-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
