cm:Concept: us-gaap:ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments
| Servicing Asset at Amortized Cost, Other than Temporary Impairments |
| us-gaap:ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments |
| Amount of other-than-temporary impairment (OTTI) applied to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ServicingAssetAtAmortizedCostOtherThanTemporaryImpairments |