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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 110,330	$ 78,960	$ 211,314	$ 150,464
Preferred Stock Dividends	2,250	2,250	4,500	4,500
Net Income (Loss) Available to Common Stockholders	$ 108,080	$ 76,710	$ 206,814	$ 145,964
Basic income per common share	$ 1.02	$ 0.71	$ 1.94	$ 1.36
Diluted income per common share	$ 1.01	$ 0.71	$ 1.93	$ 1.36
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.	$ 110,330	$ 78,960	$ 211,314	$ 150,464
Preferred Stock Dividends	2,250	2,250	4,500	4,500
Net Income (Loss) Available to Common Stockholders	108,080	76,710	206,814	145,964
Less income allocated to nonvested restricted stockholders	1,139	943	2,260	1,888
Net income available to common stockholders	$ 106,941	$ 75,767	$ 204,554	$ 144,076
Weighted average common shares outstanding	105,686	105,583	105,660	105,486
Basic income per common share	$ 1.02	$ 0.71	$ 1.94	$ 1.36
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	$ 108,080	$ 76,710	$ 206,814	$ 145,964
Less income allocated to nonvested restricted stockholders	1,136	941	2,254	1,883
Net income available to common stockholders	$ 106,944	$ 75,769	$ 204,560	$ 144,081
Weighted average common shares outstanding	105,686	105,583	105,660	105,486
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	343	360	338	389
Weighted average diluted common shares outstanding	106,029	105,943	105,998	105,875
Diluted income per common share	$ 1.01	$ 0.71	$ 1.93	$ 1.36