Fair Value Measurements (Summary of Changes in Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified
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12 Months Ended |
Dec. 31, 2014
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Dec. 31, 2013
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
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|
Beginning balance |
$ 184,271us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue |
$ 194,394us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue |
Total gains or losses (realized/unrealized) included in earnings |
19,259us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 |
(2,737)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 |
Total gains losses (realized/unrealized) included in other comprehensive income |
3,638us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss |
3,253us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss |
Investment securities called |
(38,225)cbsh_InvestmentSecuritiesCalled |
(2,150)cbsh_InvestmentSecuritiesCalled |
Discount accretion |
2,006cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetDiscountAccretion |
207cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetDiscountAccretion |
Purchases of private equity securities |
14,152cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfPrivateEquitySecurities |
3,950cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfPrivateEquitySecurities |
Sale / paydown of private equity securities |
(32,464)cbsh_SalesAndRepaymentsOfPrivateEquitySecurities |
(12,865)cbsh_SalesAndRepaymentsOfPrivateEquitySecurities |
Capitalized interest/dividends |
144cbsh_CapitalizedInterestOrDividends |
331cbsh_CapitalizedInterestOrDividends |
Purchase of risk participation agreement |
41cbsh_PurchaseOfRiskParticipationAgreement |
0cbsh_PurchaseOfRiskParticipationAgreement |
Sale of risk participation agreement |
(321)cbsh_SaleOfRiskParticipationAgreement |
(112)cbsh_SaleOfRiskParticipationAgreement |
Ending balance |
152,501us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue |
184,271us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue |
Total gains or losses for the annual period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at period end |
836cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements |
(5,063)cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements |
State and Municipal Obligations [Member] |
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|
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
Beginning balance |
127,724us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
126,414us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Total gains or losses (realized/unrealized) included in earnings |
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Total gains losses (realized/unrealized) included in other comprehensive income |
3,638us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
3,253us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Investment securities called |
(38,225)cbsh_InvestmentSecuritiesCalled / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
(2,150)cbsh_InvestmentSecuritiesCalled / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Discount accretion |
2,006cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetDiscountAccretion / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
207cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetDiscountAccretion / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Purchases of private equity securities |
0cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
0cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Sale / paydown of private equity securities |
0cbsh_SalesAndRepaymentsOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
0cbsh_SalesAndRepaymentsOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Capitalized interest/dividends |
0cbsh_CapitalizedInterestOrDividends / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
0cbsh_CapitalizedInterestOrDividends / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Purchase of risk participation agreement |
0cbsh_PurchaseOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
0cbsh_PurchaseOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Sale of risk participation agreement |
0cbsh_SaleOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
0cbsh_SaleOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Ending balance |
95,143us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
127,724us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Total gains or losses for the annual period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at period end |
0cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
0cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Private Equity Investments [Member] |
|
|
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
Beginning balance |
56,612us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
68,167us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Total gains or losses (realized/unrealized) included in earnings |
19,137us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
(2,971)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Total gains losses (realized/unrealized) included in other comprehensive income |
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Investment securities called |
0cbsh_InvestmentSecuritiesCalled / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
0cbsh_InvestmentSecuritiesCalled / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Discount accretion |
0cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetDiscountAccretion / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
0cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetDiscountAccretion / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Purchases of private equity securities |
14,152cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
3,950cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Sale / paydown of private equity securities |
(32,464)cbsh_SalesAndRepaymentsOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
(12,865)cbsh_SalesAndRepaymentsOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Capitalized interest/dividends |
144cbsh_CapitalizedInterestOrDividends / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
331cbsh_CapitalizedInterestOrDividends / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Purchase of risk participation agreement |
0cbsh_PurchaseOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
0cbsh_PurchaseOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Sale of risk participation agreement |
0cbsh_SaleOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
0cbsh_SaleOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Ending balance |
57,581us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
56,612us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Total gains or losses for the annual period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at period end |
718cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
(5,297)cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements / us-gaap_FairValueByAssetClassAxis = us-gaap_PrivateEquityFundsMember |
Derivatives [Member] |
|
|
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
Beginning balance |
(65)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
(187)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Total gains or losses (realized/unrealized) included in earnings |
122us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
234us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Total gains losses (realized/unrealized) included in other comprehensive income |
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Investment securities called |
0cbsh_InvestmentSecuritiesCalled / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
0cbsh_InvestmentSecuritiesCalled / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Discount accretion |
0cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetDiscountAccretion / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
0cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetDiscountAccretion / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Purchases of private equity securities |
0cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
0cbsh_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchaseOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Sale / paydown of private equity securities |
0cbsh_SalesAndRepaymentsOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
0cbsh_SalesAndRepaymentsOfPrivateEquitySecurities / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Capitalized interest/dividends |
0cbsh_CapitalizedInterestOrDividends / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
0cbsh_CapitalizedInterestOrDividends / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Purchase of risk participation agreement |
41cbsh_PurchaseOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
0cbsh_PurchaseOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Sale of risk participation agreement |
(321)cbsh_SaleOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
(112)cbsh_SaleOfRiskParticipationAgreement / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Ending balance |
(223)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
(65)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
Total gains or losses for the annual period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at period end |
$ 118cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |
$ 234cbsh_ChangeInUnrealizedGainsOrLossesRelatedToAssetsHeldLevel3FairValueMeasurements / us-gaap_FairValueByAssetClassAxis = cbsh_DerivativeLevelThreeUnobservableInputsMember |