Common Stock (Summary Of Components Used To Calculate Basic And Diluted Income Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 68,224	$ 66,006	$ 195,046	$ 202,538
Basic income per common share	$ 0.75	$ 0.71	$ 2.14	$ 2.18
Diluted income per common share	$ 0.75	$ 0.72	$ 2.14	$ 2.18
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.	68,224	66,006	195,046	202,538
Less income allocated to nonvested restricted stockholders	808	626	2,152	1,854
Net income available to common stockholders	67,416	65,380	192,894	200,684
Weighted average common shares outstanding	90,003	91,239	89,999	91,879
Basic income per common share	$ 0.75	$ 0.71	$ 2.14	$ 2.18
Diluted 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.	68,224	66,006	195,046	202,538
Less income allocated to nonvested restricted stockholders	806	623	2,146	1,849
Net income available to common stockholders	$ 67,418	$ 65,383	$ 192,900	$ 200,689
Weighted average common shares outstanding	90,003	91,239	89,999	91,879
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	449	313	353	316
Weighted average diluted common shares outstanding	90,452	91,552	90,352	92,195
Diluted income per common share	$ 0.75	$ 0.72	$ 2.14	$ 2.18