Name:	cbsh_EstimatedReductionInOverdraftIncome
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Company's estimate of loss related to 10 basis point reduction in credit card interchange fees for the future 8-month period, which is required under a preliminary settlement. The 8-month period has not yet been announced, as the settlment has not yet been finalized. During 2012, the Company recorded a reserve for this estimated loss.

No definition available.

Name:	cbsh_LossDueToReductionInCreditCardInterchangeFees
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Number of days after court ordered period before the start of the credit card interchange reduction included in the proposed settlement. The court-orded period has not yet been announced.

No definition available.

Name:	cbsh_NumberOfDaysUntilStartOfReductionAfterCourtOrderedPeriod
Namespace Prefix:	cbsh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Number of months during which the reduction of the credit card interchange is effective, as agreed in the propsed settlement agreement. The reduction period will begin at a court-specified future date, which has not yet been announced.

No definition available.

Name:	cbsh_NumberOfMonthsOfInterchangeReduction
Namespace Prefix:	cbsh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

If this percentage of affected merchants opt out of the proposed agreement, the agreement could be cancelled.

No definition available.

Name:	cbsh_PercentOfOptOutMerchantsThatCouldCauseAgreementToCancel
Namespace Prefix:	cbsh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Total proposed cash payment for all defendants in the settlement.

No definition available.

Name:	cbsh_SettlementCashPaymentAllParties
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Visa's share of the proposed settlement's cash payout.

No definition available.

Name:	cbsh_SettlementCashPaymentVisaShare
Namespace Prefix:	cbsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

This element represents the expenses incurred by the entity which are directly related and attributable to receiving an award in settlement of litigation.

No definition available.

Name:	us-gaap_LitigationSettlementExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

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