Common Stock (Summary Of Components Used To Calculate Basic And Diluted Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic income per common share	$ 1.06	$ 1.02	$ 3.18	$ 2.87
Diluted income per common share	$ 1.06	$ 1.01	$ 3.18	$ 2.86
Basic income per common share:
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 141,518	$ 138,007	$ 425,589	$ 390,223
Less income allocated to nonvested restricted stock	1,338	1,289	4,058	3,646
Net income allocated to common stock	$ 140,180	$ 136,718	$ 421,531	$ 386,577
Weighted average common shares outstanding	132,338	134,217	132,568	134,862
Basic income per common share	$ 1.06	$ 1.02	$ 3.18	$ 2.87
Diluted income per common share:
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Commerce Bancshares, Inc.	$ 141,518	$ 138,007	$ 425,589	$ 390,223
Less income allocated to nonvested restricted stock	1,337	1,288	4,055	3,643
Net income allocated to common stock	$ 140,181	$ 136,719	$ 421,534	$ 386,580
Weighted average common shares outstanding	132,338	134,217	132,568	134,862
Net effect of the assumed exercise of stock-based awards - based on the treasury stock method using the average market price for the respective periods	125	178	136	163
Weighted average diluted common shares outstanding	132,463	134,395	132,704	135,025
Diluted income per common share	$ 1.06	$ 1.01	$ 3.18	$ 2.86