| Standard label: | Transfers and Servicing of Financial Assets, Transfers of Financial Assets, Sales, Policy [Policy Text Block] |
| Name: | us-gaap:TransfersAndServicingOfFinancialAssetsTransfersOfFinancialAssetsSalesPolicy |
| Documentation: | Disclosure of accounting policy for recognizing whether a transfer of a financial asset qualifies for sale treatment, and its initial and subsequent accounting for a sale transaction. If an entity has securitized financial assets during any period presented and accounts for that transfer as a sale, for each major asset type (for example, mortgage loans, credit card receivables, and automobile loans), the entity generally discloses its accounting policies for initially and subsequently measuring any interests that it obtains and sells, or those it continues to hold in the transaction, including the methodology (for example, quoted market prices) and significant assumptions used to value such interests, and the gains and losses resulting from the sale. |
| Object type: | cm:Level2TextBlock |
| 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:TransfersAndServicingOfFinancialAssetsTransfersOfFinancialAssetsSalesPolicy |
| Label | Role | Language |
| Transfers and Servicing of Financial Assets, Transfers of Financial Assets, Sales, Policy [Policy Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 235 10 50 3 | http://fasb.org/us-gaap/role/ref/legacyRef | 235 |
| FASB Accounting Standards Codification 860 10 50 4 | http://fasb.org/us-gaap/role/ref/legacyRef | 860 |
| FASB Accounting Standards Codification 860 20 50 4 (a) | http://fasb.org/us-gaap/role/ref/legacyRef | 860 |