Parent Company Condensed Financial Statements (Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
OPERATING ACTIVITIES:
Net income		$ 566,251	$ 526,331	$ 477,060
Other changes, net		(2,769)	(15,986)	(113,481)
Net cash provided by (used in) operating activities		645,136	577,859	488,769
INVESTING ACTIVITIES
Proceeds from maturities/pay downs of investment securities	[1]	1,774,612	2,133,113	1,935,552
Purchases of investment securities	[1]	(1,451,271)	(2,677,996)	(246,286)
Purchases of land, buildings and equipment		(52,748)	(46,133)	(88,074)
Net cash provided by (used in) investing activities		(462,370)	483,787	2,183,832
FINANCING ACTIVITIES
Purchases of treasury stock		(207,567)	(170,470)	(76,370)
Net cash provided by (used in) financing activities		(11,043)	(372,937)	(883,119)
Increase (decrease) in cash and cash equivalents		171,723	688,709	1,789,482
Income tax payments (receipts), net		162,912	126,129	130,957
Commerce Bancshares, Inc. (Parent) [Member]
OPERATING ACTIVITIES:
Net income		566,251	526,331	477,060
Earnings of consolidated subsidiaries, net of dividends		(338,060)	(191,421)	(203,570)
Other changes, net		10,312	(165,330)	5,749
Net cash provided by (used in) operating activities		238,503	169,580	279,239
INVESTING ACTIVITIES
(Increase) Decrease In Investment In Subsidiaries, Net		(10)	0	4,348
Proceeds from sales and maturities of available for sale debt, equity, and other securities		0	176,561	0
Proceeds from maturities/pay downs of investment securities		7,433	9	15
Purchases of investment securities		(862)	(1,062)	(902)
(Increase) Decrease In Advances To Subsidiaries Net		950	300	18,729
Purchases of land, buildings and equipment		(38)	(5)	(490)
Net cash provided by (used in) investing activities		7,473	175,803	21,700
FINANCING ACTIVITIES
Purchases of treasury stock		(207,567)	(171,407)	(76,890)
Issuance of stock under equity compensation plans		(4)	0	(3)
Cash dividends paid on common stock		(146,596)	(139,503)	(134,734)
Net cash provided by (used in) financing activities		(354,167)	(310,910)	(211,627)
Increase (decrease) in cash and cash equivalents		(108,191)	34,473	89,312
Cash and cash equivalents at beginning of year		357,046	322,573	233,261
Cash and cash equivalents at end of year		248,855	357,046	322,573
Income tax payments (receipts), net		$ (4,430)	$ 34,975	$ (3,254)

[1] Available for sale debt securities, equity securities, and other securities.