cm:Level2TextBlock: us-gaap:FinancingReceivableAllowanceForCreditLossesPolicyOrMethodologyChangePolicyTextBlock
| Financing Receivable, Allowance for Credit Losses, Policy or Methodology Change [Policy Text Block] |
| us-gaap:FinancingReceivableAllowanceForCreditLossesPolicyOrMethodologyChangePolicyTextBlock |
| Disclosure of accounting policy for recognizing any changes to a creditor's accounting policies or methodology from the prior period and management's rationale for the change. |
| cm:Level2TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:FinancingReceivableAllowanceForCreditLossesPolicyOrMethodologyChangePolicyTextBlock |