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Commitments and Contingent Liabilities (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Loss Contingencies [Line Items]      
Operating Leases, Rent Expense, Net $ 25,000,000us-gaap_OperatingLeasesRentExpenseNet $ 23,500,000us-gaap_OperatingLeasesRentExpenseNet $ 21,700,000us-gaap_OperatingLeasesRentExpenseNet
Operating Leases, Future Minimum Payments, Due in 2015 26,000,000us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent    
Operating Leases, Future Minimum Payments, Due in 2016 22,900,000us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears    
Operating Leases, Future Minimum Payments, Due in 2017 19,300,000us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears    
Operating Leases, Future Minimum Payments, Due in 2018 15,100,000us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears    
Operating Leases, Future Minimum Payments, Due in 2019 13,000,000us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears    
Operating Leases, Future Minimum Payments, Due Thereafter 104,800,000us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter    
Minimum Average Cash Balance Required to be Maintained at Federal Reserve by Subsidiary Bank 1,500,000,000bokf_MinimumAverageCashBalanceRequiredToBeMaintainedAtFederalReserveBySubsidiaryBank 830,000,000bokf_MinimumAverageCashBalanceRequiredToBeMaintainedAtFederalReserveBySubsidiaryBank  
Parent Company [Member] | Visa Membership [Member]      
Loss Contingencies [Line Items]      
Number of Visa Class B Shares Owned by Entity (in shares) 251,837bokf_CommonStockClassBSharesOwned
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= bokf_VisaMembershipMember
   
Number of Visa Class A Shares Visa Class B Shares Are Convertible To (in shares) 103,782bokf_NumberofVisaClassASharesVisaClassBSharesAreConvertibleTo
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= bokf_VisaMembershipMember
   
Cavanal Hill Funds [Member]      
Loss Contingencies [Line Items]      
Mutual Fund Investment in US Treasury Securities 1,100,000,000bokf_MutualFundAssetsManagedInvestmentInUsTreasurySecurities
/ dei_LegalEntityAxis
= bokf_CavanalHillFundsMember
   
Mutual Fund Investment in Cash Management 1,300,000,000bokf_MutualFundAssetsManagedInCashManagement
/ dei_LegalEntityAxis
= bokf_CavanalHillFundsMember
   
Mutual Fund Investment in Tax-Free Money Market Funds $ 258,000,000bokf_MutualFundManagedAssetsInTaxFreeMoneyMarketFunds
/ dei_LegalEntityAxis
= bokf_CavanalHillFundsMember
   
The Net Asset Value of Units in Mutual Funds (per unit) 1.00bokf_MutualFundsManagedNetAssetValueOfUnitsInMutualFunds
/ dei_LegalEntityAxis
= bokf_CavanalHillFundsMember