Summary of Consolidation Policy (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) mi²	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) mi²	Jun. 30, 2014 USD ($)	Jan. 01, 2015
Maximum [Member] | Decoupling Mechanism [Member]
Schedule of Capitalization, Equity [Line Items]
Public Utilities, Rate Case, Approved Effective Annual Rate Percentage Increase (Decrease)					3.00%
Subsidiaries [Member]
Schedule of Capitalization, Equity [Line Items]
Area of Service Territory (in sqmi)	6,000		6,000
Excise taxes collected | $	$ 50.3	$ 50.6	$ 119.9	$ 128.5