Common Stock Common Stock (Accelerated Share Repurchase) (Details) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended
Jun. 30, 2014
Common Stock (Accelerated Share Repurchase) [Abstract]
Accelerated Share Repurchase Program Repurchase Amount	$ 200.0
Accelerated Share Repurchase, percentage of total repurchase delivered	70.00%
Shares received under accelerated share repurchase program	3,055,434

Accelerated Share Repurchase, percentage of total repurchase delivered as of period end.

No definition available.

Name:	cbsh_AcceleratedShareRepurchasepercentageoftotalrepurchasedelivered
Namespace Prefix:	cbsh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration