Parent Company Condensed Financial Statements (Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income	$ 276,854	$ 266,975	$ 262,784
Other changes, net	(26,666)	(11,189)	(3,242)
Net cash provided by (used in) operating activities	432,367	289,063	360,836
Proceeds from sales of available for sale securities	24,380	689,031	64,442
Proceeds from maturities/pay downs of available for sale securities	2,032,397	2,515,113	1,914,105
Purchases of investment securities	(1,988,101)	(3,542,537)	(2,498,090)
Purchases of land, buildings and equipment	(24,478)	(31,897)	(43,658)
Net cash provided by (used in) investing activities	(805,213)	(1,195,402)	(1,062,682)
Proceeds from issuance of preferred stock	0	0	144,784
Purchases of treasury stock	(39,381)	(23,176)	(70,974)
Net tax benefit related to equity compensation plans	3,390	2,132	1,850
Cash dividends paid on common stock	(87,070)	(84,961)	(84,241)
Cash dividends paid on preferred stock	(9,000)	(9,000)	(4,050)
Net cash provided by (used in) financing activities	652,562	308,341	533,049
Increase (decrease) in cash and cash equivalents	279,716	(597,998)	(168,797)
Cash and cash equivalents at beginning of year	502,719	1,100,717	1,269,514
Cash and cash equivalents at end of year	782,435	502,719	1,100,717
Income tax payments (receipts), net	119,596	95,341	120,172
Commerce Bancshares, Inc. (Parent) [Member]
Net income	275,391	263,730	261,754
Earnings of consolidated subsidiaries, net of dividends	(118,704)	(106,636)	(32,493)
Other changes, net	6,151	(3,284)	5,412
Net cash provided by (used in) operating activities	162,838	153,810	234,673
(Increase) decrease in securities purchased under agreements to resell	(51,335)	57,210	(19,000)
(Increase) decrease in investment in subsidiaries, net	4	(6)	357
Proceeds from sales of available for sale securities	2,949	0	157
Proceeds from maturities/pay downs of available for sale securities	4,105	3,516	5,852
Purchases of investment securities	0	(2,500)	0
(Increase) decrease in advances to subsidiaries, net	13,507	1,171	(17,959)
Purchases of land, buildings and equipment	(3)	(113)	(98)
Net cash provided by (used in) investing activities	(30,773)	59,278	(30,691)
Proceeds from issuance of preferred stock	0	0	144,784
Purchases of treasury stock	(39,381)	(23,176)	(70,974)
Accelerated stock repurchase agreement	0	(100,000)	(200,000)
Issuance under stock purchase and equity compensation plans	(6)	1,914	8,652
Net tax benefit related to equity compensation plans	3,390	2,132	1,850
Cash dividends paid on common stock	(87,070)	(84,961)	(84,241)
Cash dividends paid on preferred stock	(9,000)	(9,000)	(4,050)
Net cash provided by (used in) financing activities	(132,067)	(213,091)	(203,979)
Increase (decrease) in cash and cash equivalents	(2)	(3)	3
Cash and cash equivalents at beginning of year	53	56	53
Cash and cash equivalents at end of year	51	53	56
Income tax payments (receipts), net	$ (8,958)	$ 1,278	$ (8,209)