| Standard label: | Transfers and Servicing of Financial Assets, Policy [Policy Text Block] |
| Name: | us-gaap:TransfersAndServicingOfFinancialAssetsPolicyTextBlock |
| Documentation: | Disclosure of accounting policy for transfers and servicing financial assets, including securitization transactions as well as repurchase and resale agreements. This disclosure may include how the entity (1) determines whether a transaction is accounted for as a sale; (2) accounts for a sale transaction, including the initial and subsequent accounting for any interests that the entity obtains or continues to hold in the transaction, how such interests are valued, and the significant assumptions used in the valuation; (3) accounts for a transaction that does not qualify for sale treatment (that is, a financing); and (4) accounts for its servicing assets and liabilities ("servicing"), including how such servicing is measured initially and subsequently, and the methodology and significant assumptions used to value such servicing. |
| 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:TransfersAndServicingOfFinancialAssetsPolicyTextBlock |
| Label | Role | Language |
| Transfers and Servicing of Financial Assets, 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 2 | 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 |
| FASB Accounting Standards Codification 860 30 50 1A | http://fasb.org/us-gaap/role/ref/legacyRef | 860 |
| FASB Accounting Standards Codification 860 50 50 2 (a) | http://fasb.org/us-gaap/role/ref/legacyRef | 860 |
| FASB Accounting Standards Codification 860 50 50 3 (a) | http://fasb.org/us-gaap/role/ref/legacyRef | 860 |
| FASB Accounting Standards Codification 860 50 50 4 (a) | http://fasb.org/us-gaap/role/ref/legacyRef | 860 |