cm:Level2TextBlock: us-gaap:OffBalanceSheetCreditExposurePolicyPolicyTextBlock
| Off-Balance-Sheet Credit Exposure, Policy [Policy Text Block] |
| us-gaap:OffBalanceSheetCreditExposurePolicyPolicyTextBlock |
| Description of accounting policies and methodologies used to estimate the entity's liability for off-balance sheet credit exposures and related charges for those credit exposures. |
| cm:Level2TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:OffBalanceSheetCreditExposurePolicyPolicyTextBlock |