Common Stock (Summary Of Components Used To Calculate Basic And Diluted Income Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 66,006	$ 65,352	$ 202,538	$ 194,839
Basic income per common share	$ 0.75	$ 0.72	$ 2.29	$ 2.14
Diluted income per common share	$ 0.75	$ 0.72	$ 2.29	$ 2.13
Diluted 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.	66,006	65,352	202,538	194,839
Less income allocated to nonvested restricted stockholders	623	486	1,849	1,388
Net income available to common stockholders	65,383	64,866	200,689	193,451
Weighted average common shares outstanding	86,894	89,477	87,504	90,373
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	298	260	300	351
Weighted average diluted common shares outstanding	87,192	89,737	87,804	90,724
Diluted income per common share	$ 0.75	$ 0.72	$ 2.29	$ 2.13
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.	66,006	65,352	202,538	194,839
Less income allocated to nonvested restricted stockholders	626	486	1,854	1,391
Net income available to common stockholders	$ 65,380	$ 64,866	$ 200,684	$ 193,448
Weighted average common shares outstanding	86,894	89,477	87,504	90,373
Basic income per common share	$ 0.75	$ 0.72	$ 2.29	$ 2.14