XML 130 R114.htm IDEA: XBRL DOCUMENT
v3.20.4

Employee Benefit Plans (Assumptions On A Weighted Average Basis, Used In Accounting For Plans) (Details) | 12 Months Ended
--- | ---
Dec. 31, 2020 Rate | Dec. 31, 2019 Rate | Dec. 31, 2018 Rate
Defined Benefit Plan, Assumptions Used in Calculations [Abstract] |  |  |
Determination of benefit obligation at year end, Discount rate | 2.25% | 3.07% | 4.14%
Determination of benefit obligation at year end, Assumed credit on cash balance accounts | 5.00% | 5.00% | 5.00%
Determination of net periodic benefit cost for year ended, Discount rate | 3.08% | 4.13% | 3.57%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Effective Rate of Interest | 2.69% | 3.81% | 3.28%
Determination of net periodic benefit cost for year ended, Long-term rate of return on assets | 5.00% | 5.00% | 5.00%
Determination of net periodic benefit cost for year ended, Assumed credit on cash balance accounts | 5.00% | 5.00% | 5.00%

X
- Definition Defined benefit plan assumptions used calculating benefit obligation, assumed credit on cash balance accounts. + References No definition available. + Details
Name: | cbsh_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationAssumedCreditOnCashBalanceAccounts
Namespace Prefix: | cbsh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Defined benefit plan assumptions used calculating net periodic benefit cost assumed credit on cash balance accounts. + References No definition available. + Details
Name: | cbsh_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostAssumedCreditOnCashBalanceAccounts
Namespace Prefix: | cbsh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Effective rate of interest used to determine net periodic benefit cost of defined benefit plan. + References No definition available. + Details
Name: | cbsh_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostEffectiveRateofInterest
Namespace Prefix: | cbsh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedInCalculationsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration