Regulatory Capital Requirements (Schedule Of Capital Amounts And Ratios On Consolidated Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Total Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	10.00%
Tier I Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	8.00%
Tier I Common Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	6.50%
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	$ 3,189,432	$ 3,052,079
Total Capital (to risk-weighted assets), Actual Ratio	14.82%	15.48%
Total Capital (to risk-weighted assets), Minimum Capital Requirement Amount	$ 1,721,317	$ 1,577,105
Total Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	8.00%	8.00%
Tier I Capital (to risk-weighted assets), Actual Amount	$ 2,950,926	$ 2,890,322
Tier I Capital (to risk-weighted assets), Actual Ratio	13.71%	14.66%
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Amount	$ 1,290,988	$ 1,182,829
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	6.00%	6.00%
Tier I Common Capital (to risk-weighted assets), Actual Amount	$ 2,950,926	$ 2,745,538
Tier I Common Capital (to rIsk-weighted assets), Actual Rato	13.71%	13.93%
Tier I Common Capital (to risk-weighted assets), Minimum Capital Requirement Amount	$ 968,241	$ 887,122
Tier I Common Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	4.50%	4.50%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Amount	$ 2,950,926	$ 2,890,322
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Ratio	9.45%	11.38%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Amount	$ 1,249,584	$ 1,015,771
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	$ 2,844,675	$ 2,583,676
Total Capital (to risk-weighted assets), Actual Ratio	13.30%	13.19%
Total Capital (to risk-weighted assets), Minimum Capital Requirement Amount	$ 1,710,778	$ 1,566,866
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	$ 2,138,472	$ 1,958,583
Total Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	10.00%	10.00%
Tier I Capital (to risk-weighted assets), Actual Amount	$ 2,606,169	$ 2,421,919
Tier I Capital (to risk-weighted assets), Actual Ratio	12.19%	12.37%
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Amount	$ 1,283,083	$ 1,175,150
Tier I Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	6.00%	6.00%
Tier I Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Amount	$ 1,710,778	$ 1,566,866
Tier I Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	8.00%	8.00%
Tier I Common Capital (to risk-weighted assets), Actual Amount	$ 2,606,169	$ 2,421,919
Tier I Common Capital (to rIsk-weighted assets), Actual Rato	12.19%	12.37%
Tier I Common Capital (to risk-weighted assets), Minimum Capital Requirement Amount	$ 962,312	$ 881,362
Tier I Common Capital (to risk-weighted assets), Minimum Capital Requirement Ratio	4.50%	4.50%
Tier I Common Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Amount	$ 1,390,007	$ 1,273,079
Tier I Common Capital (to risk-weighted assets), Well-Capitalized Capital Requirement Ratio	6.50%	6.50%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Amount	$ 2,606,169	$ 2,421,919
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Actual Ratio	8.36%	9.57%
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Minimum Capital Requirement Amount	$ 1,246,470	$ 1,012,232
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	$ 1,558,087	$ 1,265,290
Tier I Capital (to adjusted quarterly average assets) (Leverage Ratio), Well-Capitalized Capital Requirement Ratio	5.00%	5.00%

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Amount of total capital as defined by regulatory framework.

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