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		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 70,733	$ 69,034	$ 136,532	$ 129,487
Basic income per common share	$ 0.80	$ 0.76	$ 1.54	$ 1.42
Diluted income per common share	$ 0.80	$ 0.75	$ 1.54	$ 1.41
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.	70,733	69,034	136,532	129,487
Less income allocated to nonvested restricted stockholders	665	499	1,226	902
Net income available to common stockholders	70,068	68,535	135,306	128,585
Weighted average common shares outstanding	87,404	90,866	87,812	90,829
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	268	408	302	397
Weighted average diluted common shares outstanding	87,672	91,274	88,114	91,226
Diluted income per common share	$ 0.80	$ 0.75	$ 1.54	$ 1.41
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.	70,733	69,034	136,532	129,487
Less income allocated to nonvested restricted stockholders	666	501	1,228	905
Net income available to common stockholders	$ 70,067	$ 68,533	$ 135,304	$ 128,582
Weighted average common shares outstanding	87,404	90,866	87,812	90,829
Basic income per common share	$ 0.80	$ 0.76	$ 1.54	$ 1.42