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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share	$ 1.03	$ 1.00	$ 2.96	$ 3.38
Diluted income per common share	$ 1.02	$ 0.99	$ 2.95	$ 3.37
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.	$ 122,823	$ 122,561	$ 356,771	$ 415,859
Less income allocated to nonvested restricted stock	1,119	1,114	3,241	3,792
Net income allocated to common stock	$ 121,704	$ 121,447	$ 353,530	$ 412,067
Weighted average common shares outstanding	118,895	121,628	119,619	121,889
Basic income per common share	$ 1.03	$ 1.00	$ 2.96	$ 3.38
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.	$ 122,823	$ 122,561	$ 356,771	$ 415,859
Less income allocated to nonvested restricted stock	1,118	1,112	3,236	3,785
Net income allocated to common stock	$ 121,705	$ 121,449	$ 353,535	$ 412,074
Weighted average common shares outstanding	118,895	121,628	119,619	121,889
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	264	253	274	294
Weighted average diluted common shares outstanding	119,159	121,881	119,893	122,183
Diluted income per common share	$ 1.02	$ 0.99	$ 2.95	$ 3.37