v3.25.2
Capital and Regulatory Matters - Actual and Required Capital Ratios (Detail) - USD ($)
$ in Thousands
Jun. 30, 2025
Dec. 31, 2024
Cullen/Frost [Member]    
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Common Equity Tier 1 to Risk-Weighted Assets, Actual, Capital Amount $ 4,522,416 $ 4,343,666
Common Equity Tier 1 to Risk-Weighted Assets, Actual , Ratio 13.98% 13.62%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,264,455 $ 2,232,822
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 7.00% 7.00%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount $ 4,667,868 $ 4,489,118
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio 14.43% 14.07%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,749,695 $ 2,711,283
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 8.50% 8.50%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount $ 1,940,961 $ 1,913,847
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio 6.00% 6.00%
Total Capital to Risk-Weighted Assets, Actual, Capital Amount $ 5,135,590 $ 4,954,136
Total Capital to Risk-Weighted Assets, Actual, Ratio 15.88% 15.53%
Total Capital to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 3,396,683 $ 3,349,232
Total Capital to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 10.50% 10.50%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount $ 3,234,936 $ 3,189,745
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio 10.00% 10.00%
Leverage Ratio, Actual, Capital Amount $ 4,667,868 $ 4,489,118
Leverage Ratio, Actual, Ratio 8.98% 8.63%
Leverage Ratio, Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,080,263 $ 2,079,715
Leverage Ratio, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 4.00% 4.00%
Frost Bank [Member]    
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]    
Common Equity Tier 1 to Risk-Weighted Assets, Actual, Capital Amount $ 4,536,485 $ 4,387,862
Common Equity Tier 1 to Risk-Weighted Assets, Actual , Ratio 14.03% 13.76%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,263,613 $ 2,231,710
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 7.00% 7.00%
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Capital Amount $ 2,101,926 $ 2,072,302
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 $ 4,536,485 $ 4,387,862
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio 14.03% 13.76%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,748,673 $ 2,709,934
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 8.50% 8.50%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount $ 2,586,986 $ 2,550,526
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 $ 4,864,207 $ 4,692,880
Total Capital to Risk-Weighted Assets, Actual, Ratio 15.04% 14.72%
Total Capital to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 3,395,419 $ 3,347,565
Total Capital to Risk-Weighted Assets, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 10.50% 10.50%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount $ 3,233,732 $ 3,188,157
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio 10.00% 10.00%
Leverage Ratio, Actual, Capital Amount $ 4,536,485 $ 4,387,862
Leverage Ratio, Actual, Ratio 8.72% 8.44%
Leverage Ratio, Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,080,532 $ 2,079,965
Leverage Ratio, Minimum Capital Required Plus Capital Conservation Buffer, Ratio 4.00% 4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount $ 2,600,665 $ 2,599,956
Leverage Ratio, Required to be Considered Well Capitalized, Ratio 5.00% 5.00%