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, 2020	Mar. 31, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 51,857	$ 97,138
Less Preferred Stock Dividends	2,250	2,250
Net Income (Loss) Available to Common Stockholders	$ 49,607	$ 94,888
Basic income per common share	$ 0.44	$ 0.81
Diluted income per common share	$ 0.44	$ 0.81
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.	$ 51,857	$ 97,138
Less Preferred Stock Dividends	2,250	2,250
Net Income (Loss) Available to Common Stockholders	49,607	94,888
Less income allocated to nonvested restricted stockholders	470	944
Net income available to common stockholders	$ 49,137	$ 93,944
Weighted average common shares outstanding	111,118	115,511
Basic income per common share	$ 0.44	$ 0.81
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	$ 49,607	$ 94,888
Less income allocated to nonvested restricted stockholders	469	943
Net income available to common stockholders	$ 49,138	$ 93,945
Weighted average common shares outstanding	111,118	115,511
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	258	305
Weighted average diluted common shares outstanding	111,376	115,816
Diluted income per common share	$ 0.44	$ 0.81