Principles Of Consolidation And Presentation Narrative (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Amortization Method Qualified Affordable Housing Project Investments Amortization	$ 497

Amount of amortization expense of investment in qualified affordable housing projects.

No definition available.

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