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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 109,242	$ 112,576	$ 314,351	$ 323,890
Preferred Stock Dividends	2,250	2,250	6,750	6,750
Net Income (Loss) Available to Common Stockholders	$ 106,992	$ 110,326	$ 307,601	$ 317,140
Basic income per common share	$ 0.98	$ 0.99	$ 2.79	$ 2.83
Diluted income per common share	$ 0.98	$ 0.98	$ 2.79	$ 2.82
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.	$ 109,242	$ 112,576	$ 314,351	$ 323,890
Preferred Stock Dividends	2,250	2,250	6,750	6,750
Net Income (Loss) Available to Common Stockholders	106,992	110,326	307,601	317,140
Less income allocated to nonvested restricted stockholders	1,040	1,161	2,996	3,421
Net income available to common stockholders	$ 105,952	$ 109,165	$ 304,605	$ 313,719
Weighted average common shares outstanding	107,602	110,889	109,024	110,925
Basic income per common share	$ 0.98	$ 0.99	$ 2.79	$ 2.83
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	$ 106,992	$ 110,326	$ 307,601	$ 317,140
Less income allocated to nonvested restricted stockholders	1,039	1,159	2,991	3,413
Net income available to common stockholders	$ 105,953	$ 109,167	$ 304,610	$ 313,727
Weighted average common shares outstanding	107,602	110,889	109,024	110,925
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	254	371	270	360
Weighted average diluted common shares outstanding	107,856	111,260	109,294	111,285
Diluted income per common share	$ 0.98	$ 0.98	$ 2.79	$ 2.82