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
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 65,799	$ 60,453
Basic income per common share	$ 0.74	$ 0.66
Diluted income per common share	$ 0.74	$ 0.66
Diluted income per common share computations in unexercised stock options and stock appreciation rights		861
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.	65,799	60,453
Less income allocated to nonvested restricted stockholders	561	403
Net income available to common stockholders	65,238	60,050
Distributed income	20,247	19,907
Undistributed income	44,991	40,143
Weighted average common shares outstanding	88,221	90,791
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	335	387
Weighted average diluted common shares outstanding	88,556	91,178
Distributed income per share	$ 0.23	$ 0.22
Undistributed income per share	$ 0.51	$ 0.44
Diluted income per common share	$ 0.74	$ 0.66
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.	65,799	60,453
Less income allocated to nonvested restricted stockholders	562	404
Net income available to common stockholders	65,237	60,049
Distributed income	20,247	19,907
Undistributed income	$ 44,990	$ 40,142
Weighted average common shares outstanding	88,221	90,791
Distributed income per share	$ 0.23	$ 0.22
Undistributed income per share	$ 0.51	$ 0.44
Basic income per common share	$ 0.74	$ 0.66