AFS securities in loss position at period-end, change in unrealized loss.

No definition available.

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

- Definition

Amortized cost of available for sale debt securities that the Company sold as part of its plan to reposition a portion of its available for sale debt securities portfolio.

+ References

No definition available.

+ Details

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

- Definition

The available for sale debt securities acquired as part of the Company's plan to reposition a portion of its available for sale debt securities portfolio.

+ References

No definition available.

+ Details

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

- Definition

Estimated yield of the available for sale debt securities sold as part of the Company's plan to reposition a portion of its available for sale debt securities portfolio.

+ References

No definition available.

+ Details

Name:	cbsh_DebtSecuritiesAvailableForSalePlannedSaleYield
Namespace Prefix:	cbsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Yield of the available for sale debt securities acquired as part of the Company's plan to reposition a portion of its available for sale debt securities portfolio.

+ References

No definition available.

+ Details

Name:	cbsh_DebtSecuritiesAvailableForSalePlannedSaleYieldOfReinvestment
Namespace Prefix:	cbsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Equity Securities Sold, Average Price

+ References

No definition available.

+ Details

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

- Definition

Equity Securities Sold, Shares

+ References

No definition available.

+ Details

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

- Definition

Equity Securities without Readily Determinable Fair Value, Carrying Value

+ References

No definition available.

+ Details

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

- Definition

Equity Securities without Readily Determinable Fair Value, Shares

+ References

No definition available.

+ Details

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

- Definition

Exchange Offer, Common Shares Received

+ References

No definition available.

+ Details

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

- Definition

Exchange Offer, Conversion Rate of Common Stock. Conversion rate to Visa Class A shares from each share of Visa Class B-2 shares.

+ References

No definition available.

+ Details

Name:	cbsh_ExchangeOfferConversionRateOfCommonStock
Namespace Prefix:	cbsh_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Shares held at time of exchange offer.

+ References

No definition available.

+ Details

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

- Definition

Fair value of securities on impairment watch list.

+ References

No definition available.

+ Details

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

- Definition

The fair value of investment securities pledged for public funds, repurchase agreements, and borrowings

+ References

No definition available.

+ Details

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

- Definition

The number of investments in a single issuer that exceed 10% of stockholder's equity, excluding obligations of various government-sponsored enterprises such as FNMA, FHLB, and FHLMC.

+ References

No definition available.

+ Details

Name:	cbsh_InvestmentsExceedingTenPercentOfStockholdersEquity
Namespace Prefix:	cbsh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Loss on Available for Sale debt securities sold as part of the Company's planned AFS portfolio repositioning.

+ References

No definition available.

+ Details

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

- Definition

The percent of decrease in the fair value of securities below amortized cost requiring a review for possible impairment.

+ References

No definition available.

+ Details

Name:	cbsh_PercentageDecreaseInFairValueBelowAmortizedCost
Namespace Prefix:	cbsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

No investment in a single issuer exceeds this percentage of stockholder's equity, other than obligations of various government-sponsored enterprises such as FNMA, FHLB, and FHLMC.

+ References

No definition available.

+ Details

Name:	cbsh_PercentageOfStockholdersEquityOfWhichNoInvestmentFromSingleIssuerExceeds
Namespace Prefix:	cbsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Proceeds from Sale of Equity Securities

+ References

No definition available.

+ Details

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

- Definition

Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-9

+ Details

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479081/326-30-55-8

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-6

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-4

+ Details

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

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479106/326-30-50-4

+ Details

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

- Definition

Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-4

+ Details

Name:	us-gaap_EquitySecuritiesFvNiGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-4

+ Details

Name:	us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

+ Details

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

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AvailableforsaleSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cbsh_VisaClassB2SharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cbsh_VisaClassB3SharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cbsh_VisaClassASharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cbsh_VisaClassCSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Investment Securities (Narrative) (Details)	3 Months Ended	6 Months Ended
Investment Securities (Narrative) (Details)	Jun. 30, 2026 USD ($) $ / shares Rate shares	Jun. 30, 2026 USD ($) $ / shares Rate shares	Jun. 30, 2025 USD ($)	May 08, 2026 shares	Mar. 31, 2026 USD ($)	Dec. 31, 2025 USD ($) shares
Debt Securities, Available-for-sale [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 81,529,000	$ 81,529,000			$ 10,000,000	$ 9,803,000
Percentage decrease requiring a review for impairment		20.00%
Fair value of securities on impairment watch list	873,800,000	$ 873,800,000				896,700,000
Debt Securities, Available-for-sale, Unrealized Loss Position	6,500,435,000	6,500,435,000				5,882,003,000
Unrealized Loss on AFS Debt Securities	629,514,000	629,514,000				692,094,000
AFS securities in loss position at period-end, change in unrealized loss		(62,600,000)
Debt Securities, Available-for-Sale, Planned Sale, Amortized Cost	$ 904,700,000	$ 904,700,000
Debt Securities, Available-for-Sale, Planned Sale, Yield \| Rate	2.60%	2.60%
Loss on Available for Sale debt securities portfolio repositioning	$ 97,700,000	$ 97,700,000
Debt Securities, Available-for-Sale, Planned Sale, Reinvestment	$ 613,700,000	$ 613,700,000
Debt Securities, Available-for-Sale, Planned Sale, Yield of Reinvestment \| Rate	4.30%	4.30%
Securities pledged as collateral	$ 5,900,000,000	$ 5,900,000,000				$ 7,300,000,000
Number of investments in a single issuer that exceed 10% of stockholder's equity	0	0
No investment in a single issuer exceeds this percentage of stockholder's equity	10.00%	10.00%
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Losses realized on sales		$ 97,686,000	$ (4,218,000)
Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ 71,000,000.0	71,200,000
Equity Securities, FV-NI, Gain (Loss)		114,277,000	$ 1,777,000
Visa Class B-2 Shares
Debt Securities, Available-for-sale [Line Items]
Equity Securities without Readily Determinable Fair Value, Shares \| shares						411,723
Equity Securities without Readily Determinable Fair Value, Carrying Value						$ 0
Exchange Offer, Original Shares Held \| shares				411,723
Visa Class B-3 Shares
Debt Securities, Available-for-sale [Line Items]
Exchange Offer, Common Shares Received \| shares				205,861
Equity Securities without Readily Determinable Fair Value, Amount	$ 0	$ 0
Visa Class A Shares
Debt Securities, Available-for-sale [Line Items]
Exchange Offer, Conversion Rate of Common Stock				1.5075
Equity Securities Sold, Shares \| shares	103,000	103,000
Equity Securities Sold, Average Price \| $ / shares	$ 333.11	$ 333.11
Proceeds from Sale of Equity Securities	$ 34,500,000
Visa Class C Shares
Debt Securities, Available-for-sale [Line Items]
Equity Securities without Readily Determinable Fair Value, Shares \| shares	52,000	52,000
Exchange Offer, Common Shares Received \| shares				77,584
Equity Securities without Readily Determinable Fair Value, Amount	$ 71,000,000.0	$ 71,000,000.0