REGULATORY ASSETS AND REGULATORY LIABILITIES - Narrative (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
SJG
Regulatory Assets [Line Items]
Deferral of costs related to expected credit losses from uncollectibles	$ 7.6	$ 4.7
SJG | Environmental Remediation
Regulatory Assets [Line Items]
Original recovery period of expenditures	7 years
SJG | Judicial Ruling | Pricing dispute, long-term gas supply contract
Regulatory Assets [Line Items]
Amount paid to third party supplier		22.9
ETG Utility Operations
Regulatory Assets [Line Items]
Deferral of costs related to expected credit losses from uncollectibles	$ 12.3	$ 5.8