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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 74,353	$ 66,531	$ 135,408	$ 130,844
Preferred Stock Dividends	2,250	0	4,500	0
Net Income (Loss) Available to Common Stockholders	$ 72,103	$ 66,531	$ 130,908	$ 130,844
Basic income per common share	$ 0.75	$ 0.67	$ 1.36	$ 1.31
Diluted income per common share	$ 0.75	$ 0.66	$ 1.36	$ 1.30
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.	$ 74,353	$ 66,531	$ 135,408	$ 130,844
Preferred Stock Dividends	2,250	0	4,500	0
Net Income (Loss) Available to Common Stockholders	72,103	66,531	130,908	130,844
Less income allocated to nonvested restricted stockholders	997	856	1,793	1,658
Net income available to common stockholders	$ 71,106	$ 65,675	$ 129,115	$ 129,186
Weighted average common shares outstanding	94,380	98,206	94,832	98,855
Basic income per common share	$ 0.75	$ 0.67	$ 1.36	$ 1.31
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	$ 72,103	$ 66,531	$ 130,908	$ 130,844
Less income allocated to nonvested restricted stockholders	995	854	1,789	1,653
Net income available to common stockholders	$ 71,108	$ 65,677	$ 129,119	$ 129,191
Weighted average common shares outstanding	94,380	98,206	94,832	98,855
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	322	403	311	423
Weighted average diluted common shares outstanding	94,702	98,609	95,143	99,278
Diluted income per common share	$ 0.75	$ 0.66	$ 1.36	$ 1.30