| Standard label: | Schedule of Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Table Text Block] |
| Name: | us-gaap:ScheduleOfAssumptionsForFairValueOnSecuritizationDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrServicingLiabilitiesTextBlock |
| Documentation: | Tabular disclosure of all information related to the key inputs and assumptions used in measuring the fair value of assets obtained or liabilities incurred, as the result of a sale of financial assets, relating to the transferor's continuing involvement, if any, at the time of securitization, asset-backed financing arrangement, or similar transfer (including at a minimum, but not limited to, and if applicable, quantitative information about discount rates, expected prepayments including the expected weighted-average life of prepayable financial assets, and anticipated credit losses, including expected static pool losses). |
| Object type: | cm:Level3TextBlock |
| Data type: | Text Block (HTML) (nonnum:textBlockItemType) |
| Period type: | For Period (duration) |
| Balance type: | (no balance type) |
| Abstract: | false |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:ScheduleOfAssumptionsForFairValueOnSecuritizationDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrServicingLiabilitiesTextBlock |
| Label | Role | Language |
| Schedule of Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Table Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 860 20 50 3 (c) | http://fasb.org/us-gaap/role/ref/legacyRef | 860 |