Borrowed Funds	12 Months Ended
Dec. 31, 2013
Debt Disclosure [Abstract]
Borrowed Funds	Borrowed Funds Federal Home Loan Bank Advances. Federal Home Loan Bank (“FHLB”) advances totaled $7 thousand and had a weighted-average rate of 6.0% at December 31, 2012. These advances matured in 2013. The advances were collateralized by a blanket floating lien on all first mortgage loans, certain pledged securities, the FHLB capital stock owned by the Corporation and any funds on deposit with the FHLB. Federal Funds Purchased and Securities Sold Under Agreements to Repurchase. Federal funds purchased are short-term borrowings that typically mature within one to ninety days. Federal funds purchased totaled $200 thousand and $1.6 million at December 31, 2013 and 2012. Securities sold under agreements to repurchase are secured short-term borrowings that typically mature within thirty to ninety days. Securities sold under agreements to repurchase are stated at the amount of cash received in connection with the transaction. The Corporation may be required to provide additional collateral based on the fair value of the underlying securities. Securities sold under agreements to repurchase totaled $668.1 million and $559.5 million at December 31, 2013 and 2012. Subordinated Notes Payable. In February 2007, the Corporation issued $100 million of 5.75% fixed-to-floating rate subordinated notes that mature on February 15, 2017. The notes, which qualify as Tier 2 capital for Cullen/Frost, had an interest rate of 5.75% per annum, payable semi-annually on each February 15 and August 15, commencing on August 15, 2007 until February 15, 2012. From February 15, 2012, to but excluding the maturity date or date of earlier redemption and commencing on May 15, 2012, the notes will bear interest at a rate per annum equal to three-month LIBOR for the related interest period plus 0.53% (0.77% at December 31, 2013), payable quarterly on each February 15, May 15, August 15 and November 15. The notes are subordinated in right of payment to all our senior indebtedness and effectively subordinated to all existing and future debt and all other liabilities of our subsidiaries. The notes cannot be accelerated except in the event of bankruptcy or the occurrence of certain other events of bankruptcy, insolvency or reorganization. The notes mature on February 15, 2017. The Corporation may elect to redeem the notes (subject to regulatory approval), in whole or in part, on any interest payment date on or after February 15, 2012 at a redemption price equal to 100% of the principal amount plus any accrued and unpaid interest. Unamortized debt issuance costs related to these notes, which are included in other assets, totaled $370 thousand and $490 thousand at December 31, 2013 and 2012. Proceeds from sale of the notes were used to fund a portion of the redemption of certain junior subordinated deferrable interest debentures. Junior Subordinated Deferrable Interest Debentures. At December 31, 2013 and 2012, the Corporation had $123.7 million of junior subordinated deferrable interest debentures issued to Cullen/Frost Capital Trust II (“Trust II”), a wholly owned Delaware statutory business trust. Unamortized debt issuance costs related to Trust II, which are included in other assets, totaled $1.2 million at both December 31, 2013 and 2012. The trust is considered a variable interest entity for which the Corporation is not the primary beneficiary. Accordingly, the accounts of the trust are not included in the Corporation’s consolidated financial statements. See Note 1 - Summary of Significant Accounting Policies for additional information about the Corporation’s consolidation policy. Details of the Corporation’s transactions with the capital trust are presented below. Trust II was formed in 2004 for the purpose of issuing $120 million of floating rate (three-month LIBOR plus a margin of 1.55%) trust preferred securities, which represent beneficial interests in the assets of the trust. The trust preferred securities will mature on March 1, 2034 and are redeemable with the approval of the Federal Reserve Board in whole or in part at the option of the Corporation at any time after March 1, 2009 and in whole at any time upon the occurrence of certain events affecting their tax or regulatory capital treatment. Distributions on the trust preferred securities are payable quarterly in arrears on March 1, June 1, September 1 and December 1 of each year. Trust II also issued $3.7 million of common equity securities to Cullen/Frost. The proceeds of the offering of the trust preferred securities and common equity securities were used to purchase $123.7 million of floating rate (three-month LIBOR plus a margin of 1.55%, which was equal to 1.79% and 1.86% at December 31, 2013 and 2012) junior subordinated deferrable interest debentures issued by the Corporation, which have terms substantially similar to the trust preferred securities. In October 2008, the Corporation entered into an interest rate swap contract on the junior subordinated deferrable interest debentures that effectively fixed the interest rate on the debentures for a period of five years, terminating in October 2013. See Note 15 - Derivative Financial Instruments. The Corporation has the right at any time during the term of the debentures to defer payments of interest at any time or from time to time for an extension period not exceeding 20 consecutive quarterly periods with respect to each extension period. Under the terms of the debentures, in the event that under certain circumstances there is an event of default under the debentures or the Corporation has elected to defer interest on the debentures, the Corporation may not, with certain exceptions, declare or pay any dividends or distributions on its capital stock or purchase or acquire any of its capital stock. Payments of distributions on the trust preferred securities and payments on redemption of the trust preferred securities are guaranteed by the Corporation on a limited basis. The Corporation also entered into an agreement with the Trust II as to expenses and liabilities pursuant to which the Corporation has agreed, on a subordinated basis, to pay any costs, expenses or liabilities of Trust II other than those arising under the trust preferred securities. The obligations of the Corporation under the junior subordinated debentures, the related indenture, the trust agreement establishing the trust, the guarantee and the agreement as to expenses and liabilities, in the aggregate, constitute a full and unconditional guarantee by the Corporation of Trust II’s obligations under the trust preferred securities. Despite the fact that the accounts of the capital trusts are not included in the Corporation’s consolidated financial statements, the trust preferred securities issued by these subsidiary trusts are included in the Tier 1 capital of Cullen/Frost for regulatory capital purposes. Federal Reserve Board rules limit the aggregate amount of restricted core capital elements (which includes trust preferred securities, among other things) that may be included in the Tier 1 capital of most bank holding companies to 25% of all core capital elements, including restricted core capital elements, net of goodwill less any associated deferred tax liability. Large, internationally active bank holding companies (as defined) are subject to a 15% limitation. Amounts of restricted core capital elements in excess of these limits generally may be included in Tier 2 capital. The current quantitative limits do not preclude the Corporation from including the $120 million in trust preferred securities outstanding in Tier 1 capital as of December 31, 2013. As more fully discussed in Note 9 - Capital and Regulatory Matters, new rules related to the implementation of the Basel III capital framework will require the phase-out of certain hybrid securities, such as trust preferred securities, as Tier 1 capital of bank holding companies beginning January 1, 2015.

Borrowed Funds

Federal Home Loan Bank Advances. Federal Home Loan Bank (“FHLB”) advances totaled $7 thousand and had a weighted-average rate of 6.0% at December 31, 2012. These advances matured in 2013. The advances were collateralized by a blanket floating lien on all first mortgage loans, certain pledged securities, the FHLB capital stock owned by the Corporation and any funds on deposit with the FHLB.

Federal Funds Purchased and Securities Sold Under Agreements to Repurchase. Federal funds purchased are short-term borrowings that typically mature within one to ninety days. Federal funds purchased totaled $200 thousand and $1.6 million at December 31, 2013 and 2012. Securities sold under agreements to repurchase are secured short-term borrowings that typically mature within thirty to ninety days. Securities sold under agreements to repurchase are stated at the amount of cash received in connection with the transaction. The Corporation may be required to provide additional collateral based on the fair value of the underlying securities. Securities sold under agreements to repurchase totaled $668.1 million and $559.5 million at December 31, 2013 and 2012.

Subordinated Notes Payable. In February 2007, the Corporation issued $100 million of 5.75% fixed-to-floating rate subordinated notes that mature on February 15, 2017. The notes, which qualify as Tier 2 capital for Cullen/Frost, had an interest rate of 5.75% per annum, payable semi-annually on each February 15 and August 15, commencing on August 15, 2007 until February 15, 2012. From February 15, 2012, to but excluding the maturity date or date of earlier redemption and commencing on May 15, 2012, the notes will bear interest at a rate per annum equal to three-month LIBOR for the related interest period plus 0.53% (0.77% at December 31, 2013), payable quarterly on each February 15, May 15, August 15 and November 15. The notes are subordinated in right of payment to all our senior indebtedness and effectively subordinated to all existing and future debt and all other liabilities of our subsidiaries. The notes cannot be accelerated except in the event of bankruptcy or the occurrence of certain other events of bankruptcy, insolvency or reorganization. The notes mature on February 15, 2017. The Corporation may elect to redeem the notes (subject to regulatory approval), in whole or in part, on any interest payment date on or after February 15, 2012 at a redemption price equal to 100% of the principal amount plus any accrued and unpaid interest. Unamortized debt issuance costs related to these notes, which are included in other assets, totaled $370 thousand and $490 thousand at December 31, 2013 and 2012. Proceeds from sale of the notes were used to fund a portion of the redemption of certain junior subordinated deferrable interest debentures.

Junior Subordinated Deferrable Interest Debentures. At December 31, 2013 and 2012, the Corporation had $123.7 million of junior subordinated deferrable interest debentures issued to Cullen/Frost Capital Trust II (“Trust II”), a wholly owned Delaware statutory business trust. Unamortized debt issuance costs related to Trust II, which are included in other assets, totaled $1.2 million at both December 31, 2013 and 2012. The trust is considered a variable interest entity for which the Corporation is not the primary beneficiary. Accordingly, the accounts of the trust are not included in the Corporation’s consolidated financial statements. See Note 1 - Summary of Significant Accounting Policies for additional information about the Corporation’s consolidation policy. Details of the Corporation’s transactions with the capital trust are presented below.

Trust II was formed in 2004 for the purpose of issuing $120 million of floating rate (three-month LIBOR plus a margin of 1.55%) trust preferred securities, which represent beneficial interests in the assets of the trust. The trust preferred securities will mature on March 1, 2034 and are redeemable with the approval of the Federal Reserve Board in whole or in part at the option of the Corporation at any time after March 1, 2009 and in whole at any time upon the occurrence of certain events affecting their tax or regulatory capital treatment. Distributions on the trust preferred securities are payable quarterly in arrears on March 1, June 1, September 1 and December 1 of each year. Trust II also issued $3.7 million of common equity securities to Cullen/Frost. The proceeds of the offering of the trust preferred securities and common equity securities were used to purchase $123.7 million of floating rate (three-month LIBOR plus a margin of 1.55%, which was equal to 1.79% and 1.86% at December 31, 2013 and 2012) junior subordinated deferrable interest debentures issued by the Corporation, which have terms substantially similar to the trust preferred securities. In October 2008, the Corporation entered into an interest rate swap contract on the junior subordinated deferrable interest debentures that effectively fixed the interest rate on the debentures for a period of five years, terminating in October 2013. See Note 15 - Derivative Financial Instruments.

The Corporation has the right at any time during the term of the debentures to defer payments of interest at any time or from time to time for an extension period not exceeding 20 consecutive quarterly periods with respect to each extension period. Under the terms of the debentures, in the event that under certain circumstances there is an event of default under the debentures or the Corporation has elected to defer interest on the debentures, the Corporation may not, with certain exceptions, declare or pay any dividends or distributions on its capital stock or purchase or acquire any of its capital stock.

Payments of distributions on the trust preferred securities and payments on redemption of the trust preferred securities are guaranteed by the Corporation on a limited basis. The Corporation also entered into an agreement with the Trust II as to expenses and liabilities pursuant to which the Corporation has agreed, on a subordinated basis, to pay any costs, expenses or liabilities of Trust II other than those arising under the trust preferred securities. The obligations of the Corporation under the junior subordinated debentures, the related indenture, the trust agreement establishing the trust, the guarantee and the agreement as to expenses and liabilities, in the aggregate, constitute a full and unconditional guarantee by the Corporation of Trust II’s obligations under the trust preferred securities.

Despite the fact that the accounts of the capital trusts are not included in the Corporation’s consolidated financial statements, the trust preferred securities issued by these subsidiary trusts are included in the Tier 1 capital of Cullen/Frost for regulatory capital purposes. Federal Reserve Board rules limit the aggregate amount of restricted core capital elements (which includes trust preferred securities, among other things) that may be included in the Tier 1 capital of most bank holding companies to 25% of all core capital elements, including restricted core capital elements, net of goodwill less any associated deferred tax liability. Large, internationally active bank holding companies (as defined) are subject to a 15% limitation. Amounts of restricted core capital elements in excess of these limits generally may be included in Tier 2 capital. The current quantitative limits do not preclude the Corporation from including the $120 million in trust preferred securities outstanding in Tier 1 capital as of December 31, 2013. As more fully discussed in Note 9 - Capital and Regulatory Matters, new rules related to the implementation of the Basel III capital framework will require the phase-out of certain hybrid securities, such as trust preferred securities, as Tier 1 capital of bank holding companies beginning January 1, 2015.