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
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 100,984	$ 71,504
Preferred Stock Dividends	2,250	2,250
Net Income (Loss) Available to Common Stockholders	$ 98,734	$ 69,254
Basic income per common share	$ 0.92	$ 0.65
Diluted income per common share	$ 0.92	$ 0.65
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.	$ 100,984	$ 71,504
Preferred Stock Dividends	2,250	2,250
Net Income (Loss) Available to Common Stockholders	98,734	69,254
Less income allocated to nonvested restricted stockholders	1,121	945
Net income available to common stockholders	$ 97,613	$ 68,309
Weighted average common shares outstanding	105,634	105,389
Basic income per common share	$ 0.92	$ 0.65
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	$ 98,734	$ 69,254
Less income allocated to nonvested restricted stockholders	1,118	942
Net income available to common stockholders	$ 97,616	$ 68,312
Weighted average common shares outstanding	105,634	105,389
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	332	416
Weighted average diluted common shares outstanding	105,966	105,805
Diluted income per common share	$ 0.92	$ 0.65