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		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share	$ 0.96	$ 1.32	$ 1.93	$ 2.38
Diluted income per common share	$ 0.96	$ 1.32	$ 1.93	$ 2.38
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.	$ 115,794	$ 162,326	$ 233,948	$ 293,298
Less income allocated to nonvested restricted stock	1,052	1,478	2,122	2,678
Net income allocated to common stock	$ 114,742	$ 160,848	$ 231,826	$ 290,620
Weighted average common shares outstanding	119,655	121,971	119,988	122,022
Basic income per common share	$ 0.96	$ 1.32	$ 1.93	$ 2.38
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.	$ 115,794	$ 162,326	$ 233,948	$ 293,298
Less income allocated to nonvested restricted stock	1,050	1,475	2,118	2,673
Net income allocated to common stock	$ 114,744	$ 160,851	$ 231,830	$ 290,625
Weighted average common shares outstanding	119,655	121,971	119,988	122,022
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	265	302	278	315
Weighted average diluted common shares outstanding	119,920	122,273	120,266	122,337
Diluted income per common share	$ 0.96	$ 1.32	$ 1.93	$ 2.38