XML 156 R140.htm IDEA: XBRL DOCUMENT
v3.20.4

Fair Value Measurements (Summary of Gains and Losses on Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Trading Activity, Gains and Losses, Net [Line Items] |  |
Total gains or losses included in earnings | $ (6,922) | $ (820)
Change in unrealized gains or losses relating to assets still held at period end | (6,472) | (1,720)
Loans Fees And Sales [Member] |  |
Trading Activity, Gains and Losses, Net [Line Items] |  |
Total gains or losses included in earnings | 2,768 | (77)
Change in unrealized gains or losses relating to assets still held at period end | 3,226 | 458
Other Non-Interest Income [Member] |  |
Trading Activity, Gains and Losses, Net [Line Items] |  |
Total gains or losses included in earnings | 413 | (16)
Change in unrealized gains or losses relating to assets still held at period end | 385 | (1)
Investment Securities Gains (Losses), Net [Member] |  |
Trading Activity, Gains and Losses, Net [Line Items] |  |
Total gains or losses included in earnings | (10,103) | (727)
Change in unrealized gains or losses relating to assets still held at period end | $ (10,083) | $ (2,177)

X
- Definition Change in unrealized gains or losses related to assets held, level 3 fair measurements + References No definition available. + Details
Name: | cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements
Namespace Prefix: | cbsh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Total gains or losses included in earnings, level 3 fair measurements + References No definition available. + Details
Name: | cbsh_TotalGainsOrLossesIncludedInEarningsLevel3FairMeasurements
Namespace Prefix: | cbsh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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_TradingActivityGainsAndLossesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=cbsh_LoansFeesAndSalesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=cbsh_OtherNonInterestIncomeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=cbsh_InvestmentSecuritiesGainsLossesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |