cm:Level2TextBlock: us-gaap:RecognitionOfAssetAndLiabilityForLeaseOfAcquireePolicyTextBlock
| Recognition of Asset and Liability for Lease of Acquiree [Policy Text Block] |
| us-gaap:RecognitionOfAssetAndLiabilityForLeaseOfAcquireePolicyTextBlock |
| Disclosure of accounting policy election not to recognize asset and liability at acquisition for lease with remaining lease term of one year or less. |
| cm:Level2TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:RecognitionOfAssetAndLiabilityForLeaseOfAcquireePolicyTextBlock |