Nature of Business (Details) customers in Millions	Jun. 30, 2017 state customers regulated_gas_distributions_divisions
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of Customers, Regulated Distribution \| customers	3
Number of Divisions, Regulated Distribution \| regulated_gas_distributions_divisions	6
Number of States in which Entity Operates \| state	8

The number of states the entity operates in as of the balance sheet date.

No definition available.

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant