Parent Company Condensed Financial Statements (Condensed Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Securities purchased under agreements to resell	$ 1,050,000	$ 1,150,000
Available for sale securities	9,523,560	8,915,680
Non-marketable securities	106,875	107,324
Other assets	380,823	316,378
Total assets	23,994,280	23,072,036
Other liabilities	217,680	356,423
Total liabilities	21,660,034	20,857,639
Stockholders’ equity	2,330,193	2,210,642
Total liabilities and equity	23,994,280	23,072,036
Commerce Bancshares, Inc. (Parent) [Member]
Investment in consolidated subsidiary, Banks	2,069,369	1,952,179
Investment in consolidated subsidiaries, Non-banks	45,600	63,134
Cash	56	53
Securities purchased under agreements to resell	161,650	142,650
Available for sale securities	52,118	57,754
Non-marketable securities	1,787	3,326
Advances to subsidiaries, net of borrowings	19,731	1,772
Income tax benefits	3,848	470
Other assets	16,551	15,201
Total assets	2,370,710	2,236,539
Pension obligation	20,653	6,501
Other liabilities	19,864	19,396
Total liabilities	40,517	25,897
Stockholders’ equity	2,330,193	2,210,642
Total liabilities and equity	$ 2,370,710	$ 2,236,539