| **Condensed Consolidated Statements of Income (Unaudited) (Parenthetical) (USD $)In Millions** | 3 Months Ended | 6 Months Ended |
|------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Operating revenues**                                                                         | Â              | Â              | Â | Â |
| Gas distribution - Revenue taxes                                                               | $ 31.4         | $ 23.9         | $ 106.3 | $ 97.8 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The excise taxes collected by a public utility and reported in revenues if the amount of excise taxes is equal to 1 percent or more of such total.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 5 -Section 03 -Paragraph 1 -Subparagraph eReference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688
+ Details**Name:**us-gaap_ExciseTaxesCollected**Namespace Prefix:**us-gaap**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RevenuesAbstract**Namespace Prefix:**us-gaap**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |