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, 2022	Mar. 31, 2021
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share	$ 0.97	$ 1.06
Diluted income per common share	$ 0.97	$ 1.06
Basic income per common share:
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 118,154	$ 130,972
Less income allocated to nonvested restricted stock	1,070	1,200
Net income allocated to common stock	$ 117,084	$ 129,772
Weighted average common shares outstanding	120,324	122,073
Basic income per common share	$ 0.97	$ 1.06
Diluted income per common share:
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 118,154	$ 130,972
Less income allocated to nonvested restricted stock	1,068	1,198
Net income allocated to common stock	$ 117,086	$ 129,774
Weighted average common shares outstanding	120,324	122,073
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	292	329
Weighted average diluted common shares outstanding	120,616	122,402
Diluted income per common share	$ 0.97	$ 1.06