COMMITMENTS AND CONTINGENT LIABILITIES STORAGE AND DEMAND FEES INCLUDED IN GAS PURCHASES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Storage and Demand Fees Included in Gas Purchases [Line Items]
Demand Fees	$ 57.6	$ 54.4
NJRES [Member]
Storage and Demand Fees Included in Gas Purchases [Line Items]
Demand Fees	35.4	29.4
NJNG [Member]
Storage and Demand Fees Included in Gas Purchases [Line Items]
Demand Fees	$ 22.2	$ 25.0