Name:	cbsh_EffectOnInterestIncomeResultingFromModificationToCreditCardLoans
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Financing Receivable, Modified, Maximum Term of Payment Deferral for Forbearance and Repayment Plans

No definition available.

Name:	cbsh_FinancingReceivableModifiedMaximumTermOfPaymentDeferralForForbearanceAndRepaymentPlans
Namespace Prefix:	cbsh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Financing Receivable, Modified, Minimum Term of Payment Deferral for Forbearance and Repayment Plans

No definition available.

Name:	cbsh_FinancingReceivableModifiedMinimumTermOfPaymentDeferralForForbearanceAndRepaymentPlans
Namespace Prefix:	cbsh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Financing Receivable, Modified, Writeoff

No definition available.

Name:	cbsh_FinancingReceivableModifiedWriteoff
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

HFS Loans on non accrual status

No definition available.

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

Loans Held For Sale 90 Days Past Due and Still Accruing

No definition available.

Name:	cbsh_LoansHeldForSale90DaysPastDueandStillAccruing
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Period After Which Loans are Deemed in Default

No definition available.

Name:	cbsh_PeriodAfterWhichLoansAreDeemedInDefault
Namespace Prefix:	cbsh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Pledged Financial Instruments, Not Separately Reported, Loans Receivable, for Federal Home Loan Bank Debt

No definition available.

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

The carrying amount, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of FRB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

No definition available.

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

Residential Real Estate Acquired Through Foreclosure through Obtaining Physical Possession

No definition available.

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

Student Loans Held for Sale, Lower of Cost or Fair Value

No definition available.

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

Unpaid Principal Balance on Personal Real Estate Loans Held for Sale

No definition available.

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

Amount of writeoff of accrued interest on financing receivable recognized by reversing interest income.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3D
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-3D

Name:	us-gaap_FinancingReceivableAccruedInterestWriteoff
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

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

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amortized cost of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-16

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

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 946
-SubTopic 310
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480833/946-310-45-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(a)(4))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

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

Amount of commitment to lend additional funds to debtor experiencing financial difficulty for which creditor has modified terms of financing receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 36
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-36

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-SubTopic 40
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481746/310-40-50-1

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

Fair value portion of mortgage loans held-for-sale.

No definition available.

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

Carrying amount as of the balance sheet date of assets other than real property that were received in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-3

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11

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

Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11

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

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

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

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