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, 2026	Mar. 31, 2025
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share	$ 0.96	$ 0.93
Diluted income per common share	$ 0.96	$ 0.93
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.	$ 141,623	$ 131,592
Less income allocated to nonvested restricted stock awards	1,314	1,259
Net income allocated to common stock	$ 140,309	$ 130,333
Weighted average common shares outstanding	145,786	139,563
Basic income per common share	$ 0.96	$ 0.93
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.	$ 141,623	$ 131,592
Less income allocated to nonvested restricted stock awards	1,313	1,258
Net income allocated to common stock	$ 140,310	$ 130,334
Weighted average common shares outstanding	145,786	139,563
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	71	162
Weighted average diluted common shares outstanding	145,857	139,725
Diluted income per common share	$ 0.96	$ 0.93