SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - DEMAND FEES (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Demand fees	$ 258.0	$ 265.7	$ 243.7
ES
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Demand fees	74.6	95.4	120.5
NJNG
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Demand fees	$ 183.4	$ 170.3	$ 123.2