Leases (Components of Lease Income) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Operating Lease Income [Line Items]
Direct financing and sales-type leases	$ 39,771	$ 37,168
Operating Lease, Lease Income	18,464	16,816
Lease Income, Total	$ 58,235	53,984
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other
Operating Lease Income from Related Party [Member]
Operating Lease Income [Line Items]
Operating Lease, Lease Income	$ 0	$ 78

[Line Items] for Operating Lease Income [Table]

No definition available.

Name:	cbsh_OperatingLeaseIncomeLineItems
Namespace Prefix:	cbsh_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of lease income from operating, direct financing, and sales-type leases. Includes, but is not limited to, variable lease payments, interest income, profit (loss) recognized at commencement, and lease payments paid and payable to lessor.

+ References

+ Details

Name:	us-gaap_LeaseIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Indicates line item in statement of income or comprehensive income that includes operating lease income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479016/842-30-45-3

+ Details

Name:	us-gaap_OperatingLeaseIncomeComprehensiveIncomeExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of operating lease income from lease payments and variable lease payments paid and payable to lessor. Includes, but is not limited to, variable lease payments not included in measurement of lease receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 270
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482964/270-10-50-6A

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479016/842-30-45-3

+ Details

Name:	us-gaap_OperatingLeaseLeaseIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of profit (loss) for sales-type lease and (loss) for direct financing lease recognized at commencement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-5

+ Details

Name:	us-gaap_SalesTypeAndDirectFinancingLeasesProfitLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	cbsh_OperatingLeaseIncomeAxis=cbsh_OperatingLeaseIncomefromRelatedPartyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: