Stock-Based Compensation (Summary Of SAR Activity) (Details) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2022 USD ($) $ / shares shares
Stock Appreciation Rights [Roll Forward]
Rights Outstanding, Beginning Balance \| shares	896,348
Rights Granted \| shares	96,318
Rights Forfeited \| shares	(1,797)
Rights Expired \| shares	(257)
Rights Exercised \| shares	(23,137)
Rights Outstanding, Ending Balance \| shares	967,475
Weighted Average Exercise Price Outstanding, Beginning Balance \| $ / shares	$ 46.21
Weighted Average Exercise Price Granted \| $ / shares	70.64
Weighted Average Exercise Price Forfeited \| $ / shares	58.26
Weighted Average Exercise Price Expired \| $ / shares	57.18
Weighted Average Exercise Price Exercised \| $ / shares	44.54
Weighted Average Exercise Price Outstanding, Ending Balance \| $ / shares	$ 48.65
Weighted Average Remaining Contractual Term	6 years
Aggregate Intrinsic Value \| $	$ 22,190

ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriod

No definition available.

Name:	cbsh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriod
Namespace Prefix:	cbsh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Exercised In Period Weighted Average Exercise Price

+ References

No definition available.

+ Details

Name:	cbsh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriodWeightedAverageExercisePrice
Namespace Prefix:	cbsh_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpiredInPeriod

+ References

No definition available.

+ Details

Name:	cbsh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpiredInPeriod
Namespace Prefix:	cbsh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average exercise price for share-based awards expired during the period on the stock appreciation rights plan.

+ References

No definition available.

+ Details

Name:	cbsh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpiredInPeriodWeightedAverageExercisePrice
Namespace Prefix:	cbsh_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average exercise price for share-based awards forfeited during the period on the stock appreciation rights plan.

+ References

No definition available.

+ Details

Name:	cbsh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriodWeightedAverageExercisePrice
Namespace Prefix:	cbsh_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average exercise price for share-based awards issued during the period on the stock appreciation rights plan.

+ References

No definition available.

+ Details

Name:	cbsh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageExercisePrice
Namespace Prefix:	cbsh_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of outstanding awards on the stock appreciation rights plan that are outstanding as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	cbsh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumber
Namespace Prefix:	cbsh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average exercise price of awards of the stock appreciation rights plan at which awardees can acquire the proceeds from the sale of the award or underlying shares, as calculated by applying the disclosed pricing methodology.

+ References

No definition available.

+ Details

Name:	cbsh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageExercisePrice
Namespace Prefix:	cbsh_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit options.

+ References

No definition available.

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant