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, 2013	Mar. 31, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 61,017	$ 65,799
Basic income per common share	$ 0.67	$ 0.70
Diluted income per common share	$ 0.67	$ 0.70
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.	61,017	65,799
Less income allocated to nonvested restricted stockholders	594	562
Net income available to common stockholders	60,423	65,237
Weighted average common shares outstanding	90,211	92,632
Basic income per common share	$ 0.67	$ 0.70
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.	61,017	65,799
Less income allocated to nonvested restricted stockholders	593	561
Net income available to common stockholders	$ 60,424	$ 65,238
Weighted average common shares outstanding	90,211	92,632
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	233	352
Weighted average diluted common shares outstanding	90,444	92,984
Diluted income per common share	$ 0.67	$ 0.70