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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 112,576	$ 74,564	$ 323,890	$ 225,028
Preferred Stock Dividends	2,250	2,250	6,750	6,750
Net Income (Loss) Available to Common Stockholders	$ 110,326	$ 72,314	$ 317,140	$ 218,278
Basic income per common share	$ 1.03	$ 0.68	$ 2.97	$ 2.04
Diluted income per common share	$ 1.03	$ 0.67	$ 2.96	$ 2.03
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.	$ 112,576	$ 74,564	$ 323,890	$ 225,028
Preferred Stock Dividends	2,250	2,250	6,750	6,750
Net Income (Loss) Available to Common Stockholders	110,326	72,314	317,140	218,278
Less income allocated to nonvested restricted stockholders	1,161	862	3,421	2,750
Net income available to common stockholders	$ 109,165	$ 71,452	$ 313,719	$ 215,528
Weighted average common shares outstanding	105,608	105,628	105,643	105,534
Basic income per common share	$ 1.03	$ 0.68	$ 2.97	$ 2.04
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	$ 110,326	$ 72,314	$ 317,140	$ 218,278
Less income allocated to nonvested restricted stockholders	1,159	860	3,413	2,743
Net income available to common stockholders	$ 109,167	$ 71,454	$ 313,727	$ 215,535
Weighted average common shares outstanding	105,609	105,628	105,643	105,534
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	353	353	343	377
Weighted average diluted common shares outstanding	105,962	105,981	105,986	105,911
Diluted income per common share	$ 1.03	$ 0.67	$ 2.96	$ 2.03