v3.25.2
Document and Entity Information - $ / shares
 6 Months Ended
Jun. 30, 2025
Jul. 24, 2025
Dec. 31, 2024
Entity Information [Line Items]      
Document Type 10-Q    
Document Quarterly Report true    
Document Period End Date Jun. 30, 2025    
Document Transition Report false    
Entity File Number 001-13221    
Entity Registrant Name Cullen/Frost Bankers, Inc.    
Entity Incorporation, State or Country Code TX    
Entity Tax Identification Number 74-1751768    
Entity Address, Address Line One 111 W. Houston Street,    
Entity Address, City or Town San Antonio,    
Entity Address, State or Province TX    
Entity Address, Postal Zip Code 78205    
City Area Code (210)    
Local Phone Number 220-4011    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Common Stock, Shares Outstanding   64,325,284  
Common stock, par value $ 0.01   $ 0.01
Amendment Flag false    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus Q2    
Entity Central Index Key 0000039263    
Current Fiscal Year End Date --12-31    
Common Stock [Member] | NEW YORK STOCK EXCHANGE, INC. [Member]      
Entity Information [Line Items]      
Title of 12(b) Security Common Stock, $.01 Par Value    
Trading Symbol CFR    
Security Exchange Name NYSE    
Series B Preferred Stock [Member] | NEW YORK STOCK EXCHANGE, INC. [Member]      
Entity Information [Line Items]      
Title of 12(b) Security Depositary Shares, each representing a 1/40th interest in a share of 4.450% Non-Cumulative Perpetual Preferred Stock, Series B    
Trading Symbol CFR.PrB    
Security Exchange Name NYSE