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Loans And Allowance For Loan Losses (Allowance For Loan Losses And Related Loan Balance Disaggregated On The Basis Of Impairment Methodology) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Loans And Allowance For Loan Losses [Line Items]    
Impaired loans, Allowance for loan losses $ 6,841us-gaap_ImpairedFinancingReceivableRelatedAllowance $ 10,900us-gaap_ImpairedFinancingReceivableRelatedAllowance
All other loans, Allowance for loan losses 149,691cbsh_LoansAndLeasesReceivableAllowanceExcludingImpairedFinancingReceivableRelatedAllowance 150,632cbsh_LoansAndLeasesReceivableAllowanceExcludingImpairedFinancingReceivableRelatedAllowance
Impaired loans, Loans outstanding 81,088us-gaap_ImpairedFinancingReceivableRecordedInvestment 107,636us-gaap_ImpairedFinancingReceivableRecordedInvestment
All other loans, Loans outstanding 11,388,150cbsh_LoansAndLeasesReceivableExcludingImpairedFinancingReceivablesRecordedInvestment 10,849,200cbsh_LoansAndLeasesReceivableExcludingImpairedFinancingReceivablesRecordedInvestment
Commercial Portfolio Segment [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Impaired loans, Allowance for loan losses 4,527us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember		 8,476us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
All other loans, Allowance for loan losses 85,095cbsh_LoansAndLeasesReceivableAllowanceExcludingImpairedFinancingReceivableRelatedAllowance
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember		 85,713cbsh_LoansAndLeasesReceivableAllowanceExcludingImpairedFinancingReceivableRelatedAllowance
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
Impaired loans, Loans outstanding 55,551us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember		 78,516us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
All other loans, Loans outstanding 6,606,123cbsh_LoansAndLeasesReceivableExcludingImpairedFinancingReceivablesRecordedInvestment
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember		 6,356,550cbsh_LoansAndLeasesReceivableExcludingImpairedFinancingReceivablesRecordedInvestment
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= us-gaap_CommercialPortfolioSegmentMember
Personal Banking Portfolio Segment [Member]    
Loans And Allowance For Loan Losses [Line Items]    
Impaired loans, Allowance for loan losses 2,314us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember		 2,424us-gaap_ImpairedFinancingReceivableRelatedAllowance
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
All other loans, Allowance for loan losses 64,596cbsh_LoansAndLeasesReceivableAllowanceExcludingImpairedFinancingReceivableRelatedAllowance
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember		 64,919cbsh_LoansAndLeasesReceivableAllowanceExcludingImpairedFinancingReceivableRelatedAllowance
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
Impaired loans, Loans outstanding 25,537us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember		 29,120us-gaap_ImpairedFinancingReceivableRecordedInvestment
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember
All other loans, Loans outstanding $ 4,782,027cbsh_LoansAndLeasesReceivableExcludingImpairedFinancingReceivablesRecordedInvestment
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember		 $ 4,492,650cbsh_LoansAndLeasesReceivableExcludingImpairedFinancingReceivablesRecordedInvestment
/ cbsh_FinancingReceivableAndAllowanceInformationByPortfolioSegmentAxis
= cbsh_PersonalBankingPortfolioSegmentMember