Parent Company Condensed Financial Statements (Condensed Statements Of Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income	$ 262,784	$ 261,117	$ 271,439
Other changes, net	(3,242)	(12,494)	(10,026)
Net cash provided by operating activities	360,836	361,749	383,880
Proceeds from sales of available for sale securities	64,442	16,299	16,875
Proceeds from maturities/pay downs of available for sale securities	1,914,105	2,542,123	3,080,664
Purchases of investment securities	(2,498,090)	(2,411,153)	(3,182,857)
Purchases of land, buildings and equipment	(43,658)	(23,841)	(34,969)
Net cash provided by (used in) investing activities	(1,062,682)	(713,660)	(1,160,837)
Proceeds from issuance of preferred stock	144,784	0	0
Purchases of treasury stock	(210,974)	(69,353)	(104,909)
Accelerated stock repurchase agreement	(200,000)
Net tax benefit related to equity compensation plans	1,850	1,003	2,094
Cash dividends paid on common stock	(84,241)	(82,104)	(211,608)
Cash dividends paid on preferred stock	(4,050)	0	0
Net cash used in financing activities	533,049	841,600	1,039,231
Increase (decrease) in cash	(168,797)	489,689	262,274
Cash and cash equivalents at beginning of year	1,269,514	779,825	517,551
Cash and cash equivalents at end of year	1,100,717	1,269,514	779,825
Income tax payments (receipts), net	120,172	114,336	119,166
Commerce Bancshares, Inc. (Parent) [Member]
Net income	261,754	260,961	269,329
Earnings of consolidated subsidiaries, net of dividends	(32,493)	(62,815)	(34,467)
Other changes, net	5,412	(139)	(6,310)
Net cash provided by operating activities	234,673	198,007	228,552
(Increase) decrease in securities purchased under agreements to resell	(19,000)	(74,975)	50,400
Decrease in investment in subsidiaries, net	357	151	1,195
Proceeds from sales of available for sale securities	157	866	346
Proceeds from maturities/pay downs of available for sale securities	5,852	13,644	17,063
Purchases of investment securities	0	0	(2,000)
(Increase) decrease in advances to subsidiaries, net	(17,959)	3,732	4,136
Purchases of land, buildings and equipment	(98)	(402)	(92)
Net cash provided by (used in) investing activities	(30,691)	(56,984)	71,048
Proceeds from issuance of preferred stock	144,784	0	0
Purchases of treasury stock	(210,974)	(69,353)	(104,909)
Accelerated stock repurchase agreement	(60,000)	0	0
Issuance under stock purchase and equity compensation plans	8,652	9,426	14,820
Net tax benefit related to equity compensation plans	1,850	1,003	2,094
Cash dividends paid on common stock	(84,241)	(82,104)	(211,608)
Cash dividends paid on preferred stock	(4,050)	0	0
Net cash used in financing activities	(203,979)	(141,028)	(299,603)
Increase (decrease) in cash	3	(5)	(3)
Cash and cash equivalents at beginning of year	53	58	61
Cash and cash equivalents at end of year	56	53	58
Income tax payments (receipts), net	$ (8,209)	$ (6,933)	$ 523