cm:Level2TextBlock: us-gaap:BusinessCombinationsAndOtherPurchaseOfBusinessTransactionsPolicyTextBlock
| Business Combinations and Other Purchase of Business Transactions, Policy [Policy Text Block] |
| us-gaap:BusinessCombinationsAndOtherPurchaseOfBusinessTransactionsPolicyTextBlock |
| Disclosure of accounting policy for business combinations and other business acquisition transactions not accounted for using the purchase method, such as an exchange of shares between entities under common control. |
| cm:Level2TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:BusinessCombinationsAndOtherPurchaseOfBusinessTransactionsPolicyTextBlock |