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Loans And Allowance For Loan Losses (Credit Quality Of Commercial Loan Portfolio) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount $ 6,661,674cbsh_CommercialLoanPortfolioGrossCarryingAmount $ 6,435,066cbsh_CommercialLoanPortfolioGrossCarryingAmount
Pass [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 6,441,941cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 6,180,979cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Special Mention [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 107,437cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 116,692cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Substandard [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 77,713cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 95,852cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Non-Accrual [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 34,583cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= cbsh_NonAccrualMember		 41,543cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= cbsh_NonAccrualMember
Business [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 3,969,952cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember		 3,715,319cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
Business [Member] | Pass [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 3,871,569cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 3,618,120cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Business [Member] | Special Mention [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 62,904cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 61,916cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Business [Member] | Substandard [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 23,919cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 23,691cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Business [Member] | Non-Accrual [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 11,560cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbsh_NonAccrualMember		 11,592cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbsh_NonAccrualMember
Real Estate - Construction And Land [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 403,507cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember		 406,197cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
Real Estate - Construction And Land [Member] | Pass [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 385,831cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 372,515cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Real Estate - Construction And Land [Member] | Special Mention [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 3,865cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 1,697cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Real Estate - Construction And Land [Member] | Substandard [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 8,654cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 21,812cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Real Estate - Construction And Land [Member] | Non-Accrual [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 5,157cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= cbsh_NonAccrualMember		 10,173cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_ConstructionAndLandLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= cbsh_NonAccrualMember
Real Estate - Business [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 2,288,215cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember		 2,313,550cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
Real Estate - Business [Member] | Pass [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 2,184,541cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 2,190,344cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Real Estate - Business [Member] | Special Mention [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 40,668cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 53,079cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Real Estate - Business [Member] | Substandard [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount 45,140cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 50,349cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Real Estate - Business [Member] | Non-Accrual [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Commercial loans, carrying amount $ 17,866cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbsh_NonAccrualMember		 $ 19,778cbsh_CommercialLoanPortfolioGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbsh_BusinessRealEstateLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbsh_NonAccrualMember