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, 2024	Mar. 31, 2023
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share	$ 0.87	$ 0.91
Diluted income per common share	$ 0.86	$ 0.91
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.	$ 112,663	$ 119,452
Less income allocated to nonvested restricted stock	1,044	1,056
Net income allocated to common stock	$ 111,619	$ 118,396
Weighted average common shares outstanding	129,042	130,204
Basic income per common share	$ 0.87	$ 0.91
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.	$ 112,663	$ 119,452
Less income allocated to nonvested restricted stock	1,043	1,054
Net income allocated to common stock	$ 111,620	$ 118,398
Weighted average common shares outstanding	129,042	130,204
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	144	268
Weighted average diluted common shares outstanding	129,186	130,472
Diluted income per common share	$ 0.86	$ 0.91