Commitments and Contingent Liabilities	12 Months Ended
Commitments and Contingent Liabilities	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities [Text Block]	Commitments and Contingent Liabilities Litigation Contingencies As a member of Visa, BOK Financial is obligated for a proportionate share of certain covered litigation losses incurred by Visa under a retrospective responsibility plan. A contingent liability was recognized for the Company’s share of Visa’s covered litigation liabilities. Visa funded an escrow account to cover litigation claims, including covered litigation losses under the retrospective responsibility plan, with proceeds from its initial public offering in 2008 and from available cash. BOK Financial currently owns 252,233 Visa Class B shares which are convertible into 409,324 shares of Visa Class A shares after the final settlement of all covered litigation. Class B shares may be diluted in the future if the escrow fund is not adequate to cover future covered litigation costs. No value has been currently assigned to the Class B shares. On June 24, 2015, BOKF, NA received a complaint alleging that an employee had colluded with a bond issuer and an individual in misusing revenues pledged to municipal bonds for which BOKF, NA served as trustee under the bond indenture. The Company conducted an investigation and concluded that employees in one of its Corporate Trust offices had, with respect to a single group of affiliated bond issuances, violated Company policies and procedures by waiving financial covenants, granting forbearances and accepting without disclosure to the bondholders, debt service payments from sources other than pledged revenues. The relationship manager was terminated. The Company reported the circumstances to, and cooperated with an investigation by, the Securities and Exchange Commission ("SEC"). On September 7, 2016, BOKF, NA agreed, and the SEC entered, a consent order finding that BOKF, NA had violated Section 17(a) of the Securities Act of 1933 and Section 10(b) of the Securities Exchange Act and requiring BOKF, NA to disgorge $1,067,721 of fees and pay a civil penalty of $600,000. BOKF, NA disgorged the fees and paid the penalty. On December 28, 2015, in an action brought by the SEC, the United States District Court for the District of New Jersey entered a judgment against the principals involved in issuing the bonds, precluding the principals from denying the alleged violations of the federal securities laws and requiring the principals to pay all outstanding principal, accrued interest, and other amounts required under the bond documents, less the value of the facilities securing repayment of the bonds, subject to oversight by a court appointed monitor (“Payment Plan”). On August 26, 2016, BOKF, NA was sued in the United States District Court for New Jersey by two bondholders in a putative class action on behalf of all holders of the bonds alleging BOKF, NA participated in the fraudulent sale of securities by the principals. The New Jersey Federal District Action remains stayed with no current deadlines pending. On September 14, 2016, BOKF, NA was sued in the District Court of Tulsa County, Oklahoma by 19 bondholders alleging BOKF, NA participated in the fraudulent sale of securities by the principals. The Tulsa County District Court Action is pending on BOKF, NA’s motion to dismiss the plaintiff's Third Amended Petition. On January 8, 2020, the New Jersey District Court entered judgment against the principal individual and his wife for $36,805,051 in principal amount and $10,937,831 in pre-judgment interest. On January 17, 2020, the New Jersey Federal District Court formally terminated the Payment Plan. Management is no longer able to conclude that the individual principal and his wife will be successful in paying the obligations they have to pay the bonds in full but such obligations remain and are not dischargeable in bankruptcy. Beginning September 2020, the SEC filed multiple garnishments on entities either related to or holding assets for the debtor. If the individual principal and his wife do not have the financial ability to pay the bonds in full, a bondholder loss could become probable. Management has been advised by counsel that BOKF, NA has valid defenses to claims of bondholders and that no loss to the company is probable. No provision for losses has been made at this time. BOKF, NA estimates that, upon sale of all remaining collateral securing payment of the bonds, approximately $20 million will remain outstanding. A reasonable estimate cannot be made of the amount of any bondholder loss, though the amount of bondholder loss could be material to the company in the event a loss to the company becomes probable. On March 5, 2018, BOKF, NA was sued in the Fulton, Georgia County District Court by a Wrongful Death Judgment Creditor of one of the operators of a nursing home financed by one of the bonds which are the subject of the litigation discussed above. The judgment is alleged to total approximately $8 million in principal and interest at this time. Plaintiff alleges that BOKF, as Trustee, colluded with the borrower and others to defraud creditors of the nursing home by misleading the public about the solvency of the nursing home. Plaintiff alleges that this conduct has prevented her from collecting on her judgment. On April 19, 2019, the Court granted BOKF, NA's Motion to Dismiss. On May 3, 2019, the plaintiff filed a Motion for Reconsideration which remains pending. BOKF, NA is advised by counsel that BOKF, NA has valid defenses to the plaintiffs’ claims and no loss is probable. On March 14, 2017, BOKF, NA was sued in the United States District Court for the Northern District of Oklahoma by bondholders in a second putative class action representing a different set of municipal securities. The bondholders in this second action alleged two individuals purchased facilities from the principals who are the subject of the SEC New Jersey proceedings by means of the fraudulent sale of $60 million of municipal securities for which BOKF, NA also served as indenture trustee. On December 18, 2020, the action was dismissed with prejudice in exchange for a nominal payment. On March 7, 2017, a plaintiff filed a putative class action in the United States District Court for the Northern District of Texas alleging an extended overdraft fee charged by BOKF, NA is interest and exceeds permitted rates. On September 18, 2018, the District Court dismissed the Texas action and the plaintiff appealed the dismissal to the United States Court of Appeals for the Fifth Circuit which heard argument on October 8, 2019. On August 22, 2018, a plaintiff filed a second putative class action in the United States District Court for New Mexico making the same allegations as the Texas action. The District Court dismissed the plaintiff's action. The plaintiff has appealed to the United States Court of Appeals for the Tenth Circuit. Management is advised by counsel that a loss is not probable in either the now dismissed Texas action or the New Mexico action and that the loss, if any, cannot be reasonably estimated. On March 7, 2020, three former employees sued BOKF, NA, the Plan Committee of the BOKF, NA 401k Plan, and Cavanal Hill Investment Management, Inc., a subsidiary of BOKF, NA, alleging that the Defendants included proprietary investment products as investment options in the BOKF, NA 401k Plan, whose fees were too high and performance too low, for the purpose of earning fees. The action is brought as a putative class action on behalf of all Plan Participants. The action is pending on the defendants' motion to dismiss. Management is advised by counsel that a loss is not probable and that the loss, if any, cannot be reasonably estimated. On May 12, 2020, an accounting firm filed a putative class action in the District Court of Colorado alleging that BOKF, NA and other national banks failed to pay the agents of borrowers making application through the Bank to the Small Business Administration for Paycheck Protection Program (CARES Act) loans. The action has now been dismissed with prejudice by the plaintiff. In the ordinary course of business, BOK Financial and its subsidiaries are subject to legal actions and complaints. Management believes, based upon the opinion of counsel, that the actions and liability or loss, if any, resulting from the final outcomes of the proceedings, will not have a material effect on the Company’s financial condition, results of operations or cash flows. Alternative Investment Commitments The Company sponsors a private equity fund and invests in several tax credit entities and other funds as permitted by banking regulations. Consolidation of these investments is based on the variable interest model. At December 31, 2020, the Company has $290 million in interests in various alternative investments generally consisting of unconsolidated limited partnership interests in entities for which investment return is in the form of low income housing tax credits or other investments in merchant banking activities. The investment balance also includes $94 million in unfunded commitments included in Other liabilities on the Consolidated Balance Sheets. At December 31, 2019, the Company had $259 million in interests in various alternative investments and included $82 million in unfunded commitments in Other liabilities. Other Commitments and Contingencies Cavanal Hill Funds’ assets include U.S. Treasury and government securities money market funds. Assets of these funds consist of highly-rated, short-term obligations of the U.S. Treasury and Agencies. The net asset value of units in these funds was $1.00 at December 31, 2020. An investment in these funds is not insured by the Federal Deposit Insurance Corporation or guaranteed by BOK Financial or any of its subsidiaries. BOK Financial may, but is not obligated to purchase assets from these funds to maintain the net asset value at $1.00. No assets were purchased from the funds in 2020 or 2019. The Federal Reserve Bank requires member banks to maintain certain minimum average cash balances. Member banks may satisfy reserve balance requirements through holdings of vault cash and balances maintained directly with a Federal Reserve Bank. The combined average balance of vault cash and balances held at the Federal Reserve Bank was $727 million for the year ended December 31, 2020 and $618 million for the year ended December 31, 2019.