cm:Concept: us-gaap:SecuritiesSoldUnderAgreementsToRepurchaseMeasurementDifferenceDescription
| Securities Sold under Agreements to Repurchase, Measurement Difference Description |
| us-gaap:SecuritiesSoldUnderAgreementsToRepurchaseMeasurementDifferenceDescription |
| Description of measurement difference between recognized amounts and resulting measurement differences for securities sold under agreements to repurchase. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:SecuritiesSoldUnderAgreementsToRepurchaseMeasurementDifferenceDescription |