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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 107,971	$ 110,330	$ 205,109	$ 211,314
Preferred Stock Dividends	2,250	2,250	4,500	4,500
Net Income (Loss) Available to Common Stockholders	$ 105,721	$ 108,080	$ 200,609	$ 206,814
Basic income per common share	$ 0.96	$ 0.96	$ 1.81	$ 1.84
Diluted income per common share	$ 0.96	$ 0.96	$ 1.81	$ 1.84
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.	$ 107,971	$ 110,330	$ 205,109	$ 211,314
Preferred Stock Dividends	2,250	2,250	4,500	4,500
Net Income (Loss) Available to Common Stockholders	105,721	108,080	200,609	206,814
Less income allocated to nonvested restricted stockholders	1,012	1,139	1,956	2,260
Net income available to common stockholders	$ 104,709	$ 106,941	$ 198,653	$ 204,554
Weighted average common shares outstanding	109,487	110,970	109,747	110,943
Basic income per common share	$ 0.96	$ 0.96	$ 1.81	$ 1.84
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	$ 105,721	$ 108,080	$ 200,609	$ 206,814
Less income allocated to nonvested restricted stockholders	1,009	1,136	1,952	2,254
Net income available to common stockholders	$ 104,712	$ 106,944	$ 198,657	$ 204,560
Weighted average common shares outstanding	109,487	110,970	109,747	110,943
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	265	361	278	355
Weighted average diluted common shares outstanding	109,752	111,331	110,025	111,298
Diluted income per common share	$ 0.96	$ 0.96	$ 1.81	$ 1.84