Common Stock (Summary Of Components Used To Calculate Basic And Diluted Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share (in dollars per share)	$ 3.64	$ 3.68	$ 3.92
Diluted income per common share (in dollars per share)	$ 3.64	$ 3.67	$ 3.91
Basic Income Per Common Share [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 477,060	$ 488,399	$ 530,765
Less income allocated to nonvested restricted stockholders	4,241	4,450	4,846
Net income available to common stockholders	$ 472,819	$ 483,949	$ 525,919
Weighted average common shares outstanding	129,922	131,539	134,125
Basic income per common share (in dollars per share)	$ 3.64	$ 3.68	$ 3.92
Diluted Income Per Common Share [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income (Loss) Available to Common Stockholders, Diluted	$ 477,060	$ 488,399	$ 530,765
Less income allocated to nonvested restricted stockholders	4,237	4,442	4,838
Net income available to common stockholders	$ 472,823	$ 483,957	$ 525,927
Weighted average common shares outstanding	129,922	131,539	134,125
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	150	299	315
Weighted average diluted common shares outstanding	130,072	131,838	134,440
Diluted income per common share (in dollars per share)	$ 3.64	$ 3.67	$ 3.91