| Standard label: | Transfers and Servicing of Financial Assets, Servicing of Financial Assets, Policy [Policy Text Block] |
| Name: | us-gaap:TransfersAndServicingOfFinancialAssetsServicingOfFinancialAssetsPolicy |
| Documentation: | Disclosure of accounting policy for servicing assets and liabilities including, but not necessarily limited to: (a) how a servicing asset or servicing liability is initially recognized and measured, (b) management's basis for determining its classes of servicing assets and servicing liabilities, (c) where contractually specified fees, late fees or ancillary fees are reported in the statement of income, (d) how the entity subsequently measures each class of servicing assets and servicing liabilities (that is, by using the amortization method or fair value method), and the methodology and significant assumptions used to value such servicing, (e) for those classes subsequently measured using the amortization method, where changes in the carrying amount are reported in the statement of income and how such servicing assets and liabilities are evaluated for impairment, and (f) for those classes subsequently measured at fair value, where changes in the fair value are reported in the statement of income. |
| 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:TransfersAndServicingOfFinancialAssetsServicingOfFinancialAssetsPolicy |
| Label | Role | Language |
| Transfers and Servicing of Financial Assets, 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 50 35 1 | http://fasb.org/us-gaap/role/ref/legacyRef | 860 |
| FASB Accounting Standards Codification 860 50 50 2 (a),(c) | 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 |