Consolidated Statements Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
INTEREST INCOME
Interest and fees on loans	$ 463,511	$ 507,666	$ 556,404
Interest on loans held for sale	1,115	6,091	8,219
Interest on investment securities	219,348	212,697	223,860
Interest on short-term federal funds sold and securities purchased under agreements to resell	55	48	222
Interest on long-term securities purchased under agreements to resell	13,455	2,549
Interest on deposits with banks	487	427	807
Total interest income	697,971	729,478	789,512
INTEREST EXPENSE
Savings, interest checking and money market	25,856	29,298	31,431
Time open and C.D.'s of less than $100,000	11,352	22,871	51,982
Time open and C.D.'s of $100,000 and over	9,272	13,847	35,371
Interest on federal funds purchased and securities sold under agreements to repurchase	1,741	2,584	3,699
Interest on other borrowings	3,680	14,946	31,527
Total interest expense	51,901	83,546	154,010
Net interest income	646,070	645,932	635,502
Provision for loan losses	51,515	100,000	160,697
Net interest income after provision for loan losses	594,555	545,932	474,805
NON-INTEREST INCOME
Bank card transaction fees	157,077	148,888	122,124
Trust fees	88,313	80,963	76,831
Deposit account charges and other fees	82,651	92,637	106,362
Bond trading income	19,846	21,098	22,432
Consumer brokerage services	10,018	9,190	10,831
Loan fees and sales	7,580	23,116	21,273
Other	27,432	29,219	36,406
Total non-interest income	392,917	405,111	396,259
INVESTMENT SECURITIES GAINS (LOSSES), NET
Impairment (losses) reversals on debt securities	2,190	13,058	(32,783)
Noncredit-related losses (reversals) on securities not expected to be sold	(4,727)	(18,127)	30,310
Net impairment losses	(2,537)	(5,069)	(2,473)
Realized gains (losses) on sales and fair value adjustments	13,349	3,284	(4,722)
Investment securities gains (losses), net	10,812	(1,785)	(7,195)
NON-INTEREST EXPENSE
Salaries and employee benefits	345,325	346,550	345,779
Net occupancy	46,434	46,987	45,925
Equipment	22,252	23,324	25,472
Supplies and communication	22,448	27,113	32,156
Data processing and software	68,103	67,935	61,789
Marketing	16,767	18,161	18,231
Deposit insurance	13,123	19,246	27,373
Debit overdraft litigation	18,300
Debt extinguishment		11,784
Indemnification obligation	(4,432)	(4,405)	(2,496)
Other	68,929	74,439	67,508
Total non-interest expense	617,249	631,134	621,737
Income before income taxes	381,035	318,124	242,132
Less income taxes	121,412	96,249	73,757
Net income	259,623	221,875	168,375
Less non-controlling interest expense (income)	3,280	165	(700)
NET INCOME ATTRIBUTABLE TO COMMERCE BANCSHARES, INC.	$ 256,343	$ 221,710	$ 169,075
Net income per common share - basic	$ 2.83	$ 2.41	$ 1.88
Net income per common share - diluted	$ 2.82	$ 2.40	$ 1.87