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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 78,960	$ 69,893	$ 150,464	$ 135,267
Preferred Stock Dividends	2,250	2,250	4,500	4,500
Net Income (Loss) Available to Common Stockholders	$ 76,710	$ 67,643	$ 145,964	$ 130,767
Basic income per common share	$ 0.75	$ 0.67	$ 1.43	$ 1.29
Diluted income per common share	$ 0.75	$ 0.66	$ 1.43	$ 1.28
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.	$ 78,960	$ 69,893	$ 150,464	$ 135,267
Preferred Stock Dividends	2,250	2,250	4,500	4,500
Net Income (Loss) Available to Common Stockholders	76,710	67,643	145,964	130,767
Less income allocated to nonvested restricted stockholders	943	940	1,888	1,834
Net income available to common stockholders	$ 75,767	$ 66,703	$ 144,076	$ 128,933
Weighted average common shares outstanding	100,555	100,151	100,463	100,247
Basic income per common share	$ 0.75	$ 0.67	$ 1.43	$ 1.29
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	$ 76,710	$ 67,643	$ 145,964	$ 130,767
Less income allocated to nonvested restricted stockholders	941	938	1,883	1,831
Net income available to common stockholders	$ 75,769	$ 66,705	$ 144,081	$ 128,936
Weighted average common shares outstanding	100,555	100,151	100,463	100,247
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	344	261	370	245
Weighted average diluted common shares outstanding	100,899	100,412	100,833	100,492
Diluted income per common share	$ 0.75	$ 0.66	$ 1.43	$ 1.28