Common Stock Accelerated Share Repurchase (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Accelerated Share Repurchase [Abstract]
Accelerated stock repurchase agreement	$ 200.0
Initial shares received under accelerated share repurchase program	3,055,434
Percentage of Total Shares to be Delivered	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