Regulatory Capital Requirements (Schedule Of Capital Amounts And Ratios On Consolidated Basis) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
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	$ 2,304,206	$ 2,239,636
Total Capital (to risk-weighted assets), Actual Ratio	14.86%	15.28%
Total Capital (to risk-weighted assets), Minimum Capital Requirement Amount	1,240,732	1,172,843
Total Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	8.00%	8.00%
Tier I Capital (to risk-weighted assets), Actual Amount	2,131,169	2,061,761
Tier I Capital (to risk-weighted assets), Actual Ratio	13.74%	14.06%
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Amount	620,366	586,421
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Ratio		4.00%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Amount	2,131,169	2,061,761
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Ratio	9.36%	9.43%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Amount	910,977	874,673
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	2,026,666	1,971,850
Total Capital (to risk-weighted assets), Actual Ratio	13.16%	13.55%
Total Capital (to risk-weighted assets), Minimum Capital Requirement Amount	1,232,378	1,164,469
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	1,540,472	1,455,586
Total Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	10.00%	10.00%
Tier I Capital (to risk-weighted assets), Actual Amount	1,869,053	1,809,231
Tier I Capital (to risk-weighted assets), Actual Ratio	12.13%	12.43%
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Amount	616,189	582,234
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	924,283	873,351
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	1,869,053	1,809,231
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Ratio	8.24%	8.31%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Amount	907,807	871,050
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	$ 1,134,759	$ 1,088,812
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Well-Capitalized Capital Requirement Ratio	5.00%	5.00%