Parent Company Condensed Financial Statements (Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
OPERATING ACTIVITIES:
Net income		$ 477,060	$ 488,399	$ 530,765
Other changes, net		(113,481)	15,250	(10,486)
Net cash provided by (used in) operating activities		488,769	559,385	597,722
INVESTING ACTIVITIES
Proceeds from maturities/pay downs of investment securities	[1]	1,935,552	2,691,260	3,459,106
Purchases of investment securities	[1]	(246,286)	(2,147,862)	(5,947,891)
Purchases of land, buildings and equipment		(88,074)	(65,191)	(56,716)
Net cash provided by (used in) investing activities		2,183,832	242,271	(2,082,758)
FINANCING ACTIVITIES
Purchases of treasury stock		(76,370)	(186,622)	(129,361)
Cash dividends paid on common stock		(134,734)	(127,466)	(122,693)
Net cash provided by (used in) financing activities		(883,119)	(4,200,809)	3,573,662
Increase (decrease) in cash and cash equivalents		1,789,482	(3,399,153)	2,088,626
Income tax payments (receipts), net		130,957	116,995	119,665
Commerce Bancshares, Inc. (Parent) [Member]
OPERATING ACTIVITIES:
Net income		477,060	488,399	530,765
Earnings of consolidated subsidiaries, net of dividends		(203,570)	(203,965)	(200,461)
Other changes, net		5,749	2,557	8,842
Net cash provided by (used in) operating activities		279,239	286,991	339,146
INVESTING ACTIVITIES
(Increase) decrease in investment in subsidiaries, net		4,348	(9)	6
Proceeds from maturities/pay downs of investment securities		15	38	22
Purchases of investment securities		(902)	(4,534)	(4,786)
(Increase) decrease in advances to subsidiaries, net		18,729	19,996	(8,618)
Purchases of land, buildings and equipment		(490)	(741)	(28)
Net cash provided by (used in) investing activities		21,700	14,750	(13,404)
FINANCING ACTIVITIES
Purchases of treasury stock		(76,890)	(186,622)	(129,361)
Issuance of stock under equity compensation plans		(3)	(8)	(15)
Cash dividends paid on common stock		(134,734)	(127,466)	(122,693)
Net cash provided by (used in) financing activities		(211,627)	(314,096)	(252,069)
Increase (decrease) in cash and cash equivalents		89,312	(12,355)	73,673
Cash and cash equivalents at beginning of year		233,261	245,616	171,943
Cash and cash equivalents at end of year		322,573	233,261	245,616
Income tax payments (receipts), net		$ (3,254)	$ (587)	$ (4,808)

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