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Loans And Allowance For Credit Losses (Allowance For Loan Losses And Related Loan Balance Disaggregated On The Basis Of Impairment Methodology) (Details) $ in Thousands | Dec. 31, 2019 USD ($)
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Loans And Allowance For Loan Losses [Line Items] |
Impaired loans, Allowance for loan losses | $ 2,746
Impaired loans, Loans outstanding | 81,732
All other loans, Allowance for loan losses | 157,936
All other loans, Loans outstanding | 14,656,085
Commercial Portfolio Segment [Member] |
Loans And Allowance For Loan Losses [Line Items] |
Impaired loans, Allowance for loan losses | 1,629
Impaired loans, Loans outstanding | 64,500
All other loans, Allowance for loan losses | 90,131
All other loans, Loans outstanding | 9,233,880
Personal Banking Portfolio Segment [Member] |
Loans And Allowance For Loan Losses [Line Items] |
Impaired loans, Allowance for loan losses | 1,117
Impaired loans, Loans outstanding | 17,232
All other loans, Allowance for loan losses | 67,805
All other loans, Loans outstanding | $ 5,422,205

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- Definition Loans And Allowance For Loan Losses [Line Items] + References No definition available. + Details
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- Definition Amount of allowance for credit losses related to the recorded investment in loans not deemed to be impaired. + References No definition available. + Details
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Namespace Prefix: | cbsh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Recorded investment of loan receivables, excluding impaired financing receivables. + References No definition available. + Details
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Namespace Prefix: | cbsh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 14A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953550-111524 + Details
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- Definition Amount of allowance for credit losses related to recorded investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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- Details
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