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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 74,564	$ 68,545	$ 225,028	$ 203,812
Preferred Stock Dividends	2,250	2,250	6,750	6,750
Net Income (Loss) Available to Common Stockholders	$ 72,314	$ 66,295	$ 218,278	$ 197,062
Basic income per common share	$ 0.71	$ 0.65	$ 2.14	$ 1.94
Diluted income per common share	$ 0.71	$ 0.65	$ 2.14	$ 1.93
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.	$ 74,564	$ 68,545	$ 225,028	$ 203,812
Preferred Stock Dividends	2,250	2,250	6,750	6,750
Net Income (Loss) Available to Common Stockholders	72,314	66,295	218,278	197,062
Less income allocated to nonvested restricted stockholders	862	913	2,750	2,747
Net income available to common stockholders	$ 71,452	$ 65,382	$ 215,528	$ 194,315
Weighted average common shares outstanding	100,598	100,198	100,509	100,231
Basic income per common share	$ 0.71	$ 0.65	$ 2.14	$ 1.94
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	$ 72,314	$ 66,295	$ 218,278	$ 197,062
Less income allocated to nonvested restricted stockholders	860	912	2,743	2,743
Net income available to common stockholders	$ 71,454	$ 65,383	$ 215,535	$ 194,319
Weighted average common shares outstanding	100,598	100,198	100,509	100,231
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	336	255	358	248
Weighted average diluted common shares outstanding	100,934	100,453	100,867	100,479
Diluted income per common share	$ 0.71	$ 0.65	$ 2.14	$ 1.93