cm:Level3TextBlock: us-gaap:FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTableTextBlock
| Fair Value Disclosure of Asset and Liability Not Measured at Fair Value [Table Text Block] |
| us-gaap:FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTableTextBlock |
| Tabular disclosure of information about fair value of asset and liability not measured at fair value. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:FairValueDisclosureOfAssetAndLiabilityNotMeasuredAtFairValueTableTextBlock |