Consolidated Statements Of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INTEREST INCOME
Interest and fees on loans	$ 543,825	$ 489,956	$ 456,664
Interest on loans held for sale	1,000	1,317	191
Interest on investment securities	214,689	207,184	191,801
Interest on federal funds sold and short-term securities purchased under agreements to resell	230	78	60
Interest on long-term securities purchased under agreements to resell	15,440	13,544	13,172
Interest on deposits with banks	2,223	973	528
Total interest income	777,407	713,052	662,416
INTEREST EXPENSE
Savings, interest checking and money market	17,309	14,366	13,374
Time open and C.D.’s of less than $100,000	2,645	2,809	3,236
Time open and C.D.’s of $100,000 and over	10,859	8,545	6,051
Interest on federal funds purchased and securities sold under agreements to repurchase	9,829	3,315	1,861
Interest on other borrowings	3,086	3,968	3,574
Total interest expense	43,728	33,003	28,096
Net interest income	733,679	680,049	634,320
Provision for loan losses	45,244	36,318	28,727
Net interest income after provision for loan losses	688,435	643,731	605,593
NON-INTEREST INCOME
Bank card transaction fees	180,441	181,879	178,926
Trust fees	135,159	121,795	118,437
Deposit account charges and other fees	90,060	86,394	80,416
Noninterest Income, Other	7,996	10,655	11,476
Capital market fees	14,630	13,784	13,784
Loan fees and sales	13,948	11,412	8,228
Other	44,370	48,473	36,872
Total non-interest income	486,604	474,392	448,139
INVESTMENT SECURITIES GAINS (LOSSES), NET
Investment securities gains (losses), net	25,051	(53)	6,320
NON-INTEREST EXPENSE
Salaries and employee benefits	448,321	427,310	400,701
Net occupancy	45,612	46,290	44,788
Equipment	18,568	19,141	19,086
Supplies and communication	22,790	24,135	22,970
Data processing and software	92,246	92,722	83,944
Marketing	16,325	16,032	16,107
Deposit insurance	13,986	13,327	12,146
Community Service	34,377	3,906	3,180
Other	77,459	74,202	73,565
Total non-interest expense	769,684	717,065	676,487
Income before income taxes	430,406	401,005	383,565
Less income taxes	110,506	124,151	116,590
Net income	319,900	276,854	266,975
Less non-controlling interest expense	517	1,463	3,245
NET INCOME ATTRIBUTABLE TO COMMERCE BANCSHARES, INC.	319,383	275,391	263,730
Preferred stock dividends	9,000	9,000	9,000
Net Income (Loss) Available to Common Stockholders, Basic	$ 310,383	$ 266,391	$ 254,730
Net income per common share - basic (in dollars per share)	$ 2.90	$ 2.50	$ 2.33
Net income per common share - diluted (in dollars per share)	$ 2.89	$ 2.49	$ 2.32