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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 39,863	$ 107,971	$ 91,720	$ 205,109
Less Preferred Stock Dividends	2,250	2,250	4,500	4,500
Net Income (Loss) Available to Common Stockholders	$ 37,613	$ 105,721	$ 87,220	$ 200,609
Basic income per common share	$ 0.34	$ 0.91	$ 0.78	$ 1.72
Diluted income per common share	$ 0.34	$ 0.91	$ 0.78	$ 1.72
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.	$ 39,863	$ 107,971	$ 91,720	$ 205,109
Less Preferred Stock Dividends	2,250	2,250	4,500	4,500
Net Income (Loss) Available to Common Stockholders	37,613	105,721	87,220	200,609
Less income allocated to nonvested restricted stockholders	353	1,012	823	1,956
Net income available to common stockholders	$ 37,260	$ 104,709	$ 86,397	$ 198,653
Weighted average common shares outstanding	110,707	114,961	110,913	115,234
Basic income per common share	$ 0.34	$ 0.91	$ 0.78	$ 1.72
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	$ 37,613	$ 105,721	$ 87,220	$ 200,609
Less income allocated to nonvested restricted stockholders	354	1,009	823	1,952
Net income available to common stockholders	$ 37,259	$ 104,712	$ 86,397	$ 198,657
Weighted average common shares outstanding	110,707	114,961	110,913	115,234
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	190	279	223	292
Weighted average diluted common shares outstanding	110,897	115,240	111,136	115,526
Diluted income per common share	$ 0.34	$ 0.91	$ 0.78	$ 1.72