Parent Company Condensed Financial Statements (Narrative) (Details) (Commerce Bancshares, Inc. (Parent) [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commerce Bancshares, Inc. (Parent) [Member]
Amount borrowed and repaid under line of credit	$ 0	$ 0	$ 0
Line of Credit Facility, Maximum Borrowing Capacity	20,000,000
Investments in marketable common stock	37,400,000
Non-agency mortgage-backed securities	14,700,000
Unrealized net gain in fair value Investment	35,300,000
Net of tax unrealized gain included in stockholders' equity	21,900,000
Unrealized net of tax gain in fair value of investment securities held by subsidiaries	$ 63,200,000