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
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 97,138	$ 100,984
Preferred Stock Dividends	2,250	2,250
Net Income (Loss) Available to Common Stockholders	$ 94,888	$ 98,734
Basic income per common share	$ 0.85	$ 0.88
Diluted income per common share	$ 0.85	$ 0.88
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.	$ 97,138	$ 100,984
Preferred Stock Dividends	2,250	2,250
Net Income (Loss) Available to Common Stockholders	94,888	98,734
Less income allocated to nonvested restricted stockholders	944	1,121
Net income available to common stockholders	$ 93,944	$ 97,613
Weighted average common shares outstanding	110,011	110,916
Basic income per common share	$ 0.85	$ 0.88
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	$ 94,888	$ 98,734
Less income allocated to nonvested restricted stockholders	943	1,118
Net income available to common stockholders	$ 93,945	$ 97,616
Weighted average common shares outstanding	110,011	110,916
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	290	348
Weighted average diluted common shares outstanding	110,301	111,264
Diluted income per common share	$ 0.85	$ 0.88