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, 2017	Mar. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 71,504	$ 65,374
Preferred Stock Dividends	2,250	2,250
Net Income (Loss) Available to Common Stockholders	$ 69,254	$ 63,124
Basic income per common share	$ 0.68	$ 0.62
Diluted income per common share	$ 0.68	$ 0.62
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.	$ 71,504	$ 65,374
Preferred Stock Dividends	2,250	2,250
Net Income (Loss) Available to Common Stockholders	69,254	63,124
Less income allocated to nonvested restricted stockholders	945	894
Net income available to common stockholders	$ 68,309	$ 62,230
Weighted average common shares outstanding	100,370	100,344
Basic income per common share	$ 0.68	$ 0.62
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	$ 69,254	$ 63,124
Less income allocated to nonvested restricted stockholders	942	893
Net income available to common stockholders	$ 68,312	$ 62,231
Weighted average common shares outstanding	100,370	100,344
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	397	227
Weighted average diluted common shares outstanding	100,767	100,571
Diluted income per common share	$ 0.68	$ 0.62