Regulatory Capital Requirements (Schedule Of Capital Amounts And Ratios On Consolidated Basis) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Total Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	8.00%
Total Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	10.00%
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	4.00%
Tier I Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	6.00%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Ratio	4.00%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Well-Capitalized Capital Requirement Ratio	5.00%
Commerce Bancshares, Inc. (Consolidated) [Member]
Total Capital (to risk-weighted assets), Actual Amount	$ 2,092,141	$ 2,103,401
Total Capital (to risk-weighted assets), Actual Ratio	14.93%	16.04%
Total Capital (to risk-weighted assets), Minimum Capital Requirement Amount	1,121,252	1,049,221
Total Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	8.00%	8.00%
Tier I Capital (to risk-weighted assets), Actual Amount	1,906,203	1,928,690
Tier I Capital (to risk-weighted assets), Actual Ratio	13.60%	14.71%
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Amount	560,626	524,610
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	4.00%	4.00%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Amount	1,906,203	1,928,690
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Ratio	9.14%	9.55%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Amount	834,171	807,839
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Ratio	4.00%	4.00%
Commerce Bank [Member]
Total Capital (to risk-weighted assets), Actual Amount	1,887,251	1,840,952
Total Capital (to risk-weighted assets), Actual Ratio	13.60%	14.19%
Total Capital (to risk-weighted assets), Minimum Capital Requirement Amount	1,110,330	1,037,636
Total Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	8.00%	8.00%
Total Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Amount	1,387,912	1,297,045
Total Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	10.00%	10.00%
Tier I Capital (to risk-weighted assets), Actual Amount	1,713,752	1,678,530
Tier I Capital (to risk-weighted assets), Actual Ratio	12.35%	12.94%
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Amount	555,165	518,818
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	4.00%	4.00%
Tier I Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Amount	832,747	778,227
Tier I Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	6.00%	6.00%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Amount	1,713,752	1,678,530
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Ratio	8.26%	8.36%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Amount	829,711	802,709
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Ratio	4.00%	4.00%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Well-Capitalized Capital Requirement Amount	$ 1,037,139	$ 1,003,386
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Well-Capitalized Capital Requirement Ratio	5.00%	5.00%