| Standard label: | Schedule of Regulatory Assets [Table Text Block] |
| Name: | us-gaap:ScheduleOfRegulatoryAssetsTextBlock |
| Documentation: | Tabular disclosure of assets that are created when regulatory agencies permit public utilities to defer certain costs included in rate-setting to the balance sheet. |
| 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:ScheduleOfRegulatoryAssetsTextBlock |
| Label | Role | Language |
| Schedule of Regulatory Assets [Table Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 980 340 50 1 | http://fasb.org/us-gaap/role/ref/legacyRef | 980 |
| FASB Accounting Standards Codification 980 340 50 2 | http://fasb.org/us-gaap/role/ref/legacyRef | 980 |
| FASB Accounting Standards Codification 980 715 50 1 | http://fasb.org/us-gaap/role/ref/legacyRef | 980 |