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	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 261,754	$ 260,961	$ 269,329
Preferred Stock Dividends, Income Statement Impact	4,050	0	0
Net Income (Loss) Available to Common Stockholders, Basic	257,704	260,961	269,329
Basic income per common share (in dollars per share)	$ 2.62	$ 2.60	$ 2.64
Diluted income per common share (in dollars per share)	$ 2.61	$ 2.59	$ 2.63
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.	261,754	260,961	269,329
Preferred Stock Dividends, Income Statement Impact	4,050	0	0
Net Income (Loss) Available to Common Stockholders, Basic	257,704	260,961	269,329
Less income allocated to nonvested restricted stockholders	3,332	2,939	2,563
Net income available to common stockholders	254,372	258,022	266,766
Weighted average common shares outstanding	96,984	99,315	101,005
Basic income per common share (in dollars per share)	$ 2.62	$ 2.60	$ 2.64
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	257,704	260,961	269,329
Less income allocated to nonvested restricted stockholders	3,323	2,931	2,562
Net income available to common stockholders	$ 254,381	$ 258,030	$ 266,767
Weighted average common shares outstanding	96,984	99,315	101,005
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	400	417	308
Weighted average diluted common shares outstanding	97,384	99,732	101,313
Diluted income per common share (in dollars per share)	$ 2.61	$ 2.59	$ 2.63