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Document and Entity Information - shares
 6 Months Ended
Jun. 30, 2015
Jul. 22, 2015
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2015  
Document Fiscal Year Focus 2015  
Document Fiscal Period Focus Q2  
Trading Symbol CFR  
Entity Registrant Name CULLEN/FROST BANKERS, INC.  
Entity Central Index Key 0000039263  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   63,193,103