cm:Concept: us-gaap:CreditDerivativeCollateralHeldDirectlyOrByThirdParties
| Credit Derivative, Collateral Held Directly or by Third Parties |
| us-gaap:CreditDerivativeCollateralHeldDirectlyOrByThirdParties |
| Description of the nature of assets held either as collateral or by third parties that, upon the occurrence of specified triggering event or condition under the credit derivative, the seller can obtain and liquidate to recover amounts paid under the credit derivative. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:CreditDerivativeCollateralHeldDirectlyOrByThirdParties |