Common Stock Common Stock (Accelerated Share Repurchase) (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended
Jun. 19, 2014
Common Stock (Accelerated Share Repurchase) [Abstract]
Accelerated Share Repurchase Program Repurchase Amount	$ 200.0
Shares received under accelerated share repurchase program	3,055,434
Shares to be Delivered, Percentage Initially Delivered at Onset of ASR	70.00%

Accelerated share repurchase - shares delivered as a percentage of total shares to be delivered under the accelerated share repurchase program.

No definition available.

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