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Commitments, Contingencies And Guarantees (Schedule Of Off-Balance Sheet Instruments Commitments) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Standby letters of credit, net of participations $ 324,817us-gaap_GuaranteeObligationsMaximumExposure $ 325,623us-gaap_GuaranteeObligationsMaximumExposure
Commercial letters of credit 7,519cbsh_CommercialLettersOfCredit 11,771cbsh_CommercialLettersOfCredit
Credit Card [Member]    
Commitments to extend credit 3,517,639cbsh_CommitmentToExtendCredit
/ us-gaap_FinancialInstrumentAxis
= cbsh_CreditCardMember		 3,835,323cbsh_CommitmentToExtendCredit
/ us-gaap_FinancialInstrumentAxis
= cbsh_CreditCardMember
Other [Member]    
Commitments to extend credit $ 4,922,748cbsh_CommitmentToExtendCredit
/ us-gaap_FinancialInstrumentAxis
= us-gaap_OtherCreditDerivativesMember		 $ 4,591,468cbsh_CommitmentToExtendCredit
/ us-gaap_FinancialInstrumentAxis
= us-gaap_OtherCreditDerivativesMember