Document And Entity Information	9 Months Ended
	Sep. 30, 2012	Nov. 01, 2012
Document And Entity Information [Abstract]
Document Period End Date	Sep. 30, 2012
Document Fiscal Year Focus	2012
Document Type	10-Q
Amendment Flag	false
Document Fiscal Period Focus	Q3
Entity Registrant Name	COMMERCE BANCSHARES INC /MO/
Entity Central Index Key	0000022356
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		87,301,292