| Standard label: | Regulatory Depreciation and Amortization, Policy [Policy Text Block] |
| Name: | us-gaap:RegulatoryDepreciationAndAmortizationPolicy |
| Documentation: | Disclosure of accounting policy for systematically allocating capitalized costs to periods that benefit from the use thereof. Includes, but is not limited to, methods used, such as composite depreciation, descriptions of regulatory treatment for estimated removal and disposal costs, and description of amortization of plant-related regulatory assets. |
| 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:RegulatoryDepreciationAndAmortizationPolicy |
| Label | Role | Language |
| Regulatory Depreciation and Amortization, 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 235 10 50 4 (b),(c) | http://fasb.org/us-gaap/role/ref/legacyRef | 235 |