Parent Company Condensed Financial Statements (Condensed Statements Of Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest and dividends on investment securities	$ 188,006	$ 189,415	$ 211,682
Salaries and employee benefits	384,100	366,867	360,899
Data processing fees paid to affiliates	78,980	78,245	73,798
Other	80,765	72,603	70,226
Total expense	657,775	629,633	618,469
Income tax expense (benefit)	120,216	122,230	127,169
Net income	261,754	260,961	269,329
Commerce Bancshares, Inc. (Parent) [Member]
Dividends received from consolidated subsidiary banks	200,001	200,001	235,000
Dividends received from consolidated nonbank subsidiaries	34,000	390	0
Earnings of consolidated subsidiaries, net of dividends	32,493	62,815	34,467
Interest and dividends on investment securities	2,501	4,029	5,074
Management fees charged subsidiaries	25,806	20,701	23,658
Investment securities gains (losses)	204	1,294	346
Other	2,176	2,958	2,067
Total income	297,181	292,188	300,612
Salaries and employee benefits	26,030	20,433	24,188
Professional fees	2,363	3,538	1,950
Data processing fees paid to affiliates	3,030	2,775	2,664
Other	10,578	10,236	7,582
Total expense	42,001	36,982	36,384
Income tax expense (benefit)	(6,574)	(5,755)	(5,101)
Net income	$ 261,754	$ 260,961	$ 269,329