XML 153 R137.htm IDEA: XBRL DOCUMENT
v3.20.4

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Private equity investments, included in non-marketable securities | $ 94,368 | $ 94,122
Fair Value Hierarchy, Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Auction rate securities, available for sale | 8,000 |
Private equity investments, included in non-marketable securities | $ 94,368 | $ 94,122

X
- Definition Securities by which the interest rate is reset through an auction process. + References No definition available. + Details
Name: | cbsh_AuctionRateSecuritiesAvailableForSale
Namespace Prefix: | cbsh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The fair value as of the balance sheet date of firm holdings in private equity, mezzanine, venture capital, merchant banking, real estate and special situations investments. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969 + Details
Name: | us-gaap_FinancialInstrumentsOwnedPrincipalInvestmentsAtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |