Loans And Allowance For Loan Losses (Investment In Impaired Loans) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loans And Allowance For Loan Losses [Abstract]
Non-accrual loans	$ 44,739	$ 51,410
Restructured loans (accruing)	66,359	65,508
Total impaired loans	$ 111,098	$ 116,918

Loans classified as troubled debt restructurings but are not on non-accrual status. Includes (1) loans renewed at interest rates judged not to be market rates for new debt with similar risk, and as a result were classified as troubled debt restructurings under ASC 310-40 but continue to perform in accordance with their modified terms, (2) certain credit card loans under various debt management and assistance programs, and (3) loans classified as troubled debt restructurings because they had not been reaffirmed by the borrower in bankruptcy proceedings but for which the borrowers continue to make payments.

No definition available.

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