Common Stock (Summary Of Components Used To Calculate Basic And Diluted Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 64,612	$ 68,185	$ 200,020	$ 199,029
Preferred Stock Dividends	2,250	1,800	6,750	1,800
Net Income (Loss) Available to Common Stockholders	$ 62,362	$ 66,385	$ 193,270	$ 197,229
Basic income per common share	$ 0.67	$ 0.69	$ 2.03	$ 2.00
Diluted income per common share	$ 0.66	$ 0.69	$ 2.02	$ 1.99
Basic Income Per Common Share [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 64,612	$ 68,185	$ 200,020	$ 199,029
Preferred Stock Dividends	2,250	1,800	6,750	1,800
Net Income (Loss) Available to Common Stockholders	62,362	66,385	193,270	197,229
Less income allocated to nonvested restricted stockholders	884	879	2,677	2,537
Net income available to common stockholders	$ 61,478	$ 65,506	$ 190,593	$ 194,692
Weighted average common shares outstanding	91,989	95,104	93,874	97,591
Basic income per common share	$ 0.67	$ 0.69	$ 2.03	$ 2.00
Diluted Income Per Common Share [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income (Loss) Available to Common Stockholders, Diluted	$ 62,362	$ 66,385	$ 193,270	$ 197,229
Less income allocated to nonvested restricted stockholders	883	877	2,672	2,530
Net income available to common stockholders	$ 61,479	$ 65,508	$ 190,598	$ 194,699
Weighted average common shares outstanding	91,989	95,104	93,874	97,591
Net effect of the assumed exercise of stock-based awards - based on the treasury stock method using the average market price for the respective periods	280	412	300	419
Weighted average diluted common shares outstanding	92,269	95,516	94,174	98,010
Diluted income per common share	$ 0.66	$ 0.69	$ 2.02	$ 1.99