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, 2025	Mar. 31, 2024
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share	$ 0.98	$ 0.82
Diluted income per common share	$ 0.98	$ 0.82
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.	$ 131,592	$ 112,663
Less income allocated to nonvested restricted stock	1,259	1,044
Net income allocated to common stock	$ 130,333	$ 111,619
Weighted average common shares outstanding	132,917	135,494
Basic income per common share	$ 0.98	$ 0.82
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.	$ 131,592	$ 112,663
Less income allocated to nonvested restricted stock	1,258	1,043
Net income allocated to common stock	$ 130,334	$ 111,620
Weighted average common shares outstanding	132,917	135,494
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	155	151
Weighted average diluted common shares outstanding	133,072	135,645
Diluted income per common share	$ 0.98	$ 0.82