Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 24, 2013
Document Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3
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		60,497,866