Common and Preferred 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 433,542	$ 319,383	$ 275,391
Preferred Stock Dividends, Income Statement Impact	9,000	9,000	9,000
Net Income (Loss) Available to Common Stockholders, Basic	$ 424,542	$ 310,383	$ 266,391
Basic income per common share (in dollars per share)	$ 3.79	$ 2.77	$ 2.38
Diluted income per common share (in dollars per share)	$ 3.78	$ 2.76	$ 2.37
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.	$ 433,542	$ 319,383	$ 275,391
Preferred Stock Dividends, Income Statement Impact	9,000	9,000	9,000
Net Income (Loss) Available to Common Stockholders, Basic	424,542	310,383	266,391
Less income allocated to nonvested restricted stockholders	4,558	3,848	3,698
Net income available to common stockholders	$ 419,984	$ 306,535	$ 262,693
Weighted average common shares outstanding	110,812	110,833	110,505
Basic income per common share (in dollars per share)	$ 3.79	$ 2.77	$ 2.38
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	$ 424,542	$ 310,383	$ 266,391
Less income allocated to nonvested restricted stockholders	4,547	3,838	3,692
Net income available to common stockholders	$ 419,995	$ 306,545	$ 262,699
Weighted average common shares outstanding	110,812	110,833	110,505
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	343	391	295
Weighted average diluted common shares outstanding	111,155	111,224	110,800
Diluted income per common share (in dollars per share)	$ 3.78	$ 2.76	$ 2.37