v3.22.4
Capital and Regulatory Matters (Narrative) (Detail)
 3 Months Ended 12 Months Ended
Jan. 25, 2023
USD ($)
Nov. 19, 2020
USD ($)
$ / shares
shares
Mar. 16, 2020
USD ($)
$ / shares
Mar. 17, 2017
USD ($)
Feb. 15, 2013
USD ($)
$ / shares
shares
Mar. 31, 2020
USD ($)
shares
Dec. 31, 2022
USD ($)
quarter
$ / shares
Rate
shares
Dec. 31, 2021
USD ($)
$ / shares
Rate
shares
Dec. 31, 2020
USD ($)
shares
Jan. 01, 2020
USD ($)
Dec. 31, 2019
USD ($)
Jan. 01, 2019
Rate
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Credit loss optional transitional period under CECL             5 years          
Subordinated notes             $ 99,335,000 $ 99,178,000        
Cumulative effect of accounting change                     $ (29,252,000)  
Credit loss transitional period in years under CECL             3 years          
CECL Transition Amount             $ 46,200,000 $ 61,600,000        
Stock Redeemed or Called During Period, Value                 $ 150,000,000      
Treasury stock, shares, acquired | shares             31,351 31,317 206,951      
Treasury Stock, Value, Acquired, Cost Method             $ (4,391,000) $ (3,864,000) $ (15,785,000)      
Aggregate dividends available for payment without prior regulatory approval             $ 813,600,000          
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures | quarter             20          
Subsequent Event                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Share repurchase authorized amount $ 100,000,000                      
Stock repurchase program, period in force 1 year                      
Retained Earnings [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Cumulative effect of accounting change                   $ (29,300,000) $ (29,252,000)  
Stock Redeemed or Called During Period, Value                 $ 5,514,000      
Series A Preferred Stock [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Non-cumulative perpetual preferred stock, dividend rate percentage         5.375%              
Preferred Stock, Shares Issued | shares         6,000,000              
Preferred Stock, Aggregate Liquidation Preference, Value         $ 150,000,000              
Preferred Stock, Par or Stated Value Per Share | $ / shares         $ 0.01              
Liquidation preference per share | $ / shares     $ 25   $ 25              
Payments of Stock Issuance Costs         $ 5,500,000              
Proceeds from issuance of preferred stock         $ 144,500,000              
Stock Redeemed or Called During Period, Value     $ 150,000,000                  
Series B Preferred Stock [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Non-cumulative perpetual preferred stock, dividend rate percentage   4.45%                    
Preferred Stock, Shares Issued | shares   150,000         150,000 150,000        
Preferred Stock, Aggregate Liquidation Preference, Value   $ 150,000,000         $ 1,000 $ 1,000        
Preferred Stock, Par or Stated Value Per Share | $ / shares   $ 0.01         $ 0.01 $ 0.01        
Liquidation preference per share | $ / shares   $ 1,000                    
Number of Preferred Stock equivalent depositary shares | shares   40                    
Payments of Stock Issuance Costs   $ 4,500,000                    
Proceeds from issuance of preferred stock   $ 145,500,000                    
Series B Preferred Stock Equivalent Depositary Shares Member [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Liquidation preference per share | $ / shares   $ 25                    
Subordinated Debt [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Subordinated notes       $ 100,000,000                
Subordinated notes interest rate       4.50%                
Per year percentage of decreases in permissible portion of Subordinate Note included in Total Capital             20.00%          
Final years of the term of the notes             5 years          
Cullen/Frost [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Additional Tier 1 Capital beyond Common Equity Tier 1             $ 145,500,000 $ 145,500,000        
Non-cumulative perpetual preferred stock, dividend rate percentage   4.45%                    
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio                       4.50%
Capital Conservation Buffer                       2.50%
Effective common equity tier one capital to risk weighted assets, ratio upon full implementation             7.00% 7.00%       7.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets | Rate                       6.00%
Effective tier one capital ratio, upon full implementation             8.50% 8.50%       8.50%
Minimum ratio of Total capital to risk weighted assets | Rate             14.84% 15.45%       8.00%
Tier one risk based capital to risk weighted assets, ratio upon full implementation             10.50% 10.50%       10.50%
Minimum leverage ratio             4.00% 4.00%       4.00%
Cullen/Frost [Member] | Trust Preferred Securities Tier Two Capital Allowable Portion [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Trust preferred securities             $ 120,000,000 $ 120,000,000        
Cullen/Frost [Member] | Subordinated Debt [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Permissible Portion Of Subordinated Note Included In Capital             80,000,000 100,000,000        
Frost Bank [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Additional Tier 1 Capital beyond Common Equity Tier 1             $ 0 $ 0        
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio                       4.50%
Capital Conservation Buffer                       2.50%
Effective common equity tier one capital to risk weighted assets, ratio upon full implementation             7.00% 7.00%       7.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets | Rate                       6.00%
Effective tier one capital ratio, upon full implementation             8.50% 8.50%       8.50%
Minimum ratio of Total capital to risk weighted assets | Rate             13.80% 13.61%       8.00%
Tier one risk based capital to risk weighted assets, ratio upon full implementation             10.50% 10.50%       10.50%
Minimum leverage ratio             4.00% 4.00%       4.00%
stock repurchase 2022 plan | Treasury Stock [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Treasury stock, shares, acquired | shares             0          
stock repurchase 2021 plan | Treasury Stock [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Treasury stock, shares, acquired | shares               0        
Prior stock repurchase plans [Member] | Treasury Stock [Member]                        
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]                        
Treasury stock, shares, acquired | shares           177,834            
Treasury Stock, Value, Acquired, Cost Method           $ (13,700,000)