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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share	$ 0.96	$ 0.97	$ 2.94	$ 2.81
Diluted income per common share	$ 0.96	$ 0.97	$ 2.93	$ 2.81
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.	$ 120,596	$ 122,823	$ 367,837	$ 356,771
Less income allocated to nonvested restricted stock	1,073	1,119	3,257	3,241
Net income allocated to common stock	$ 119,523	$ 121,704	$ 364,580	$ 353,530
Weighted average common shares outstanding	123,718	124,840	123,868	125,600
Basic income per common share	$ 0.96	$ 0.97	$ 2.94	$ 2.81
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.	$ 120,596	$ 122,823	$ 367,837	$ 356,771
Less income allocated to nonvested restricted stock	1,072	1,118	3,254	3,236
Net income allocated to common stock	$ 119,524	$ 121,705	$ 364,583	$ 353,535
Weighted average common shares outstanding	123,718	124,840	123,868	125,600
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	100	277	158	288
Weighted average diluted common shares outstanding	123,818	125,117	124,026	125,888
Diluted income per common share	$ 0.96	$ 0.97	$ 2.93	$ 2.81