REGULATION, REGULATORY FILINGS (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended								24 Months Ended	12 Months Ended
	Nov. 17, 2011 Regulatory Filing [Member] BGSS [Member]	Sep. 30, 2012 CIP [Member]	Sep. 30, 2011 CIP [Member]	Sep. 30, 2009 CIP [Member]	Sep. 30, 2011 BGSS [Member]	Sep. 30, 2010 BGSS [Member]	Sep. 30, 2009 BGSS [Member]	Sep. 30, 2011 SBC [Member]	Sep. 30, 2011 EE [Member]	Sep. 30, 2011 EE [Member]	Sep. 30, 2011 RGGI [Member]	Sep. 30, 2009 AIP I and AIP II [Member]	Sep. 30, 2011 AIP I and AIP II [Member] Minimum [Member]	Sep. 30, 2011 AIP I and AIP II [Member] Maximum [Member]	Sep. 30, 2011 AIP I [Member]	Sep. 30, 2010 AIP I [Member]	Sep. 30, 2011 AIP II [Member]	Sep. 30, 2011 USF [Member]	Sep. 30, 2011 Compressed Natural Gas Vehicle Refueling Stations [Member]
Annual Recovery Amount Proposed to the Public Utility Regulatory Authority				$ 6.9									$ 4.7	$ 8.9
Annual Recovery Amount Approved by the Public Utility Regulatory Authority		3.0	12.1							21.1	9.6	70.8				4.2
Rate Increase (Decrease) Proposed to the Public Utility Regulatory Authority					(9.10%)		(17.20%)											(0.10%)
Regulatory Expenditures									26.1
Rate Increase (Decrease) Approved by the Public Utility Regulatory Authority								0.03%
Percent of Increase Decrease for the average residential heating customer						(3.50%)
Originally Filed Petition for Capital Investments to the Public Utility Regulatory Authority																			15
Amended Filed Petition for Capital Investments to the Public Utility Regulatory Authority																	60.2
Weighted Cost of Capital															7.76%		7.12%
Customer Refunds And Bill Credits	$ (71.2)					$ (110.4)