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Capital and Regulatory Matters - Actual and Required Capital Ratios (Detail) - USD ($) $ in Thousands | Mar. 31, 2017 | Dec. 31, 2016
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Cullen/Frost [Member] |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Common Equity Tier 1 to Risk-Weighted Assets, Actual, Capital Amount | $ 2,315,059 | $ 2,239,186
Common Equity Tier 1 to Risk-Weighted Assets, Actual , Ratio | 12.71% | 12.52%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount | $ 1,047,521 | $ 916,360
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Ratio | 5.75% | 5.125%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount | $ 1,275,155 | $ 1,251,425
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased In, Ratio | 7.00% | 7.00%
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Capital Amount | $ 1,184,154 | $ 1,162,213
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Ratio | 6.50% | 6.50%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount | $ 2,459,545 | $ 2,383,672
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio | 13.50% | 13.33%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount | $ 1,320,788 | $ 1,184,563
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Ratio | 7.25% | 6.625%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount | $ 1,548,402 | $ 1,519,587
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Ratio | 8.50% | 8.50%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount | $ 1,457,421 | $ 1,430,416
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio | 8.00% | 8.00%
Total Capital to Risk-Weighted Assets, Actual, Capital Amount | $ 2,845,601 | $ 2,669,717
Total Capital to Risk-Weighted Assets, Actual, Ratio | 15.62% | 14.93%
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount | $ 1,685,143 | $ 1,542,168
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase - In Schedule, Ratio | 9.25% | 8.625%
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount | $ 1,912,732 | $ 1,877,137
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Ratio | 10.50% | 10.50%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount | $ 1,821,776 | $ 1,788,020
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio | 10.00% | 10.00%
Leverage Ratio, Actual, Capital Amount | $ 2,459,545 | $ 2,383,672
Leverage Ratio, Actual, Ratio | 8.34% | 8.14%
Leverage Ratio, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount | $ 1,179,874 | $ 1,171,682
Leverage Ratio, Minimum Capital Required - Basel III Phase-In Schedule, Ratio | 4.00% | 4.00%
Leverage Ratio, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount | $ 1,179,823 | $ 1,171,573
Leverage Ratio, Minimum Capital Required - Basel III Fully Phased-In, Ratio | 4.00% | 4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount | $ 1,474,843 | $ 1,464,602
Leverage Ratio, Required to be Considered Well Capitalized, Ratio | 5.00% | 5.00%
Frost Bank [Member] |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |
Common Equity Tier 1 to Risk-Weighted Assets, Actual, Capital Amount | $ 2,347,446 | $ 2,296,480
Common Equity Tier 1 to Risk-Weighted Assets, Actual , Ratio | 12.92% | 12.88%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount | $ 1,044,474 | $ 913,460
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Ratio | 5.75% | 5.125%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount | $ 1,271,445 | $ 1,247,463
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased In, Ratio | 7.00% | 7.00%
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Capital Amount | $ 1,180,710 | $ 1,158,535
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Ratio | 6.50% | 6.50%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount | $ 2,347,446 | $ 2,296,480
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio | 12.92% | 12.88%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount | $ 1,316,945 | $ 1,180,814
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Ratio | 7.25% | 6.625%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount | $ 1,543,897 | $ 1,514,776
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Ratio | 8.50% | 8.50%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount | $ 1,453,181 | $ 1,425,889
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio | 8.00% | 8.00%
Total Capital to Risk-Weighted Assets, Actual, Capital Amount | $ 2,500,502 | $ 2,449,525
Total Capital to Risk-Weighted Assets, Actual, Ratio | 13.77% | 13.74%
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount | $ 1,680,241 | $ 1,537,286
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase - In Schedule, Ratio | 9.25% | 8.625%
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount | $ 1,907,167 | $ 1,871,194
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Ratio | 10.50% | 10.50%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount | $ 1,816,476 | $ 1,782,361
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio | 10.00% | 10.00%
Leverage Ratio, Actual, Capital Amount | $ 2,347,446 | $ 2,296,480
Leverage Ratio, Actual, Ratio | 7.97% | 7.85%
Leverage Ratio, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount | $ 1,178,399 | $ 1,170,249
Leverage Ratio, Minimum Capital Required - Basel III Phase-In Schedule, Ratio | 4.00% | 4.00%
Leverage Ratio, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount | $ 1,178,348 | $ 1,170,141
Leverage Ratio, Minimum Capital Required - Basel III Fully Phased-In, Ratio | 4.00% | 4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount | $ 1,472,998 | $ 1,462,812
Leverage Ratio, Required to be Considered Well Capitalized, Ratio | 5.00% | 5.00%

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- Definition The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The amount of excess Tier 1 Risk Based Capital (which consists of the types of financial capital considered the most reliable and liquid, primarily Shareholders' equity. Examples of Tier 1 capital are common stock or unit, preferred stock or unit that is irredeemable and noncumulative, and retained earnings) divided by risk-weighted assets which are assets that are weighted for credit risk according to a formula used by the Reserve Bank. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 + Details
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- Definition The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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- Definition The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
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