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Loans And Allowance for Credit Losses (Collateral-Dependent Loans) (Details) - Commercial Portfolio Segment [Member] - USD ($) $ in Thousands | Sep. 30, 2022 | Dec. 31, 2021
--- | --- | ---
Credit Quality Indicator [Line Items] |  |
Total | $ 3,122 | $ 4,063
Business |  |
Credit Quality Indicator [Line Items] |  |
Business | 3,122 | 4,063
Business Assets |  |
Credit Quality Indicator [Line Items] |  |
Total | 1,156 | 1,604
Business Assets | Business |  |
Credit Quality Indicator [Line Items] |  |
Business | 1,156 | 1,604
Oil & Gas Assets |  |
Credit Quality Indicator [Line Items] |  |
Total | 1,966 | 2,459
Oil & Gas Assets | Business |  |
Credit Quality Indicator [Line Items] |  |
Business | $ 1,966 | $ 2,459

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- Definition Collateral Dependent Loans, Amortized Cost + References No definition available. + Details
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Namespace Prefix: | cbsh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Collateral Dependent Loans, Business, Amortized Cost + References No definition available. + Details
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Namespace Prefix: | cbsh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition 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. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |