| Standard label: | Emission Credits or Allowances, Policy [Policy Text Block] |
| Name: | us-gaap:EmissionCreditsOrAllowancesPolicy |
| Documentation: | Disclosure of accounting policy for emission credits or allowances. Such accounting policy has generally been based on an inventory or intangible asset model. |
| 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:EmissionCreditsOrAllowancesPolicy |
| Label | Role | Language |
| Emission Credits or Allowances, 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 815 15 25 1 | http://fasb.org/us-gaap/role/ref/legacyRef | 815 |