Principles Of Consolidation And Presentation Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Amortization Method Qualified Affordable Housing Project Investments Amortization	$ 995	$ 756

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