Parent Company Condensed Financial Statements (Condensed Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale	$ 9,095,513	$ 9,136,853
Equity Securities, FV-NI and without Readily Determinable Fair Value	57,354	57,442
Other assets	852,377	837,288
Total assets	32,915,089	31,996,627
Other liabilities	458,302	443,694
Total liabilities	29,100,317	28,664,152
Stockholders’ equity	3,791,371	3,309,881
Total liabilities and equity	32,915,089	31,996,627
Commerce Bancshares, Inc. (Parent) [Member]
Investment in consolidated subsidiary, Banks	3,280,689	2,697,961
Investment in consolidated subsidiaries, Non-banks	203,879	187,404
Cash	248,855	357,046
Debt Securities, Available-for-sale	941	5,381
Equity Securities, FV-NI and without Readily Determinable Fair Value	12,337	12,750
Note receivable due from bank subsidiary	50,000	50,000
Advances to subsidiaries, net of borrowings	550	1,500
Income tax receivable and deferred tax assets	7,546	9,131
Other assets	34,004	31,164
Total assets	3,838,801	3,352,337
Pension obligation	1,277	3,220
Other liabilities	46,153	39,236
Total liabilities	47,430	42,456
Stockholders’ equity	3,791,371	3,309,881
Total liabilities and equity	$ 3,838,801	$ 3,352,337