cm:Concept: us-gaap:SecuritiesPurchasedUnderAgreementsToResellMeasurementDifferenceDescription
| Securities Purchased under Agreements to Resell, Measurement Difference Description |
| us-gaap:SecuritiesPurchasedUnderAgreementsToResellMeasurementDifferenceDescription |
| Description of measurement difference between recognized amounts and resulting measurement differences for securities purchased under agreement to resell. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:SecuritiesPurchasedUnderAgreementsToResellMeasurementDifferenceDescription |