Loans And Allowance For Credit Losses (Aging Information On Past Due And Accruing Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	$ 20,738,455	$ 17,648,771
30 - 89 Days Past Due	59,705	82,083
90 Days Past Due and Still Accruing	23,703	24,659
Non-accrual loans	11,618	15,750
Total	20,833,481	17,771,263
Business Loan [Member]
Loans And Allowance For Loan Losses [Line Items]
Total	7,115,984	6,439,380
Real estate - construction and land
Loans And Allowance For Loan Losses [Line Items]
Total	1,493,455	1,438,012
Business Real Estate Loan [Member]
Loans And Allowance For Loan Losses [Line Items]
Total	4,064,253	3,674,567
Personal Real Estate Loan [Member]
Loans And Allowance For Loan Losses [Line Items]
Total	4,369,077	3,053,435
Consumer Loan [Member]
Loans And Allowance For Loan Losses [Line Items]
Total	2,527,448	2,196,822
Revolving home equity
Loans And Allowance For Loan Losses [Line Items]
Total	649,332	375,159
Credit Card Receivable [Member]
Loans And Allowance For Loan Losses [Line Items]
Total	561,277	589,694
Overdrafts
Loans And Allowance For Loan Losses [Line Items]
Total	52,655	4,194
Commercial Portfolio Segment [Member]
Loans And Allowance For Loan Losses [Line Items]
Total	12,673,692	11,551,959
Commercial Portfolio Segment [Member] \| Business Loan [Member]
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	7,110,497	6,437,476
30 - 89 Days Past Due	4,437	1,241
90 Days Past Due and Still Accruing	958	540
Non-accrual loans	92	123
Total	7,115,984	6,439,380
Commercial Portfolio Segment [Member] \| Real estate - construction and land
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	1,493,277	1,437,727
30 - 89 Days Past Due	0	285
90 Days Past Due and Still Accruing	178	0
Non-accrual loans	0	0
Total	1,493,455	1,438,012
Commercial Portfolio Segment [Member] \| Business Real Estate Loan [Member]
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	4,039,565	3,636,517
30 - 89 Days Past Due	14,905	23,265
90 Days Past Due and Still Accruing	418	0
Non-accrual loans	9,365	14,785
Total	4,064,253	3,674,567
Personal Banking Portfolio Segment [Member]
Loans And Allowance For Loan Losses [Line Items]
Total	8,159,789	6,219,304
Personal Banking Portfolio Segment [Member] \| Personal Real Estate Loan [Member]
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	4,350,290	3,021,212
30 - 89 Days Past Due	6,417	19,450
90 Days Past Due and Still Accruing	10,242	11,931
Non-accrual loans	2,128	842
Total	4,369,077	3,053,435
Personal Banking Portfolio Segment [Member] \| Consumer Loan [Member]
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	2,498,563	2,165,109
30 - 89 Days Past Due	25,678	28,269
90 Days Past Due and Still Accruing	3,207	3,444
Non-accrual loans	0	0
Total	2,527,448	2,196,822
Personal Banking Portfolio Segment [Member] \| Revolving home equity
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	647,275	373,245
30 - 89 Days Past Due	983	1,493
90 Days Past Due and Still Accruing	1,041	421
Non-accrual loans	33	0
Total	649,332	375,159
Personal Banking Portfolio Segment [Member] \| Credit Card Receivable [Member]
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	546,617	573,698
30 - 89 Days Past Due	7,001	7,673
90 Days Past Due and Still Accruing	7,659	8,323
Non-accrual loans	0	0
Total	561,277	589,694
Personal Banking Portfolio Segment [Member] \| Overdrafts
Loans And Allowance For Loan Losses [Line Items]
Current or Less than 30 Days Past Due	52,371	3,787
30 - 89 Days Past Due	284	407
90 Days Past Due and Still Accruing	0	0
Non-accrual loans	0	0
Total	$ 52,655	$ 4,194

Financing Receivable, Recorded Investment, Current or Less than 30 days Past Due

No definition available.

Name:	cbsh_FinancingReceivableRecordedInvestmentCurrentorLessthan30daysPastDue
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivable, Recorded Investment, 30 to 89 Days Past Due

+ References

No definition available.

+ Details

Name:	cbsh_FinancingReceivableRecordedInvestmentThirtyToEightyNineDaysPastDue
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Loans And Allowance For Loan Losses [Line Items]

+ References

No definition available.

+ Details

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

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of financing receivable 90 days or more past due and still accruing. Excludes net investment in lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-7

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 80
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479294/326-20-55-80

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (3)
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (2)
-Publisher SEC

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbsh_BusinessLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbsh_ConstructionAndLandLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbsh_BusinessRealEstateLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbsh_PersonalRealEstateLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CreditCardReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbsh_OverdraftsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=cbsh_PersonalBankingPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: