LINES OF CREDIT AND SHORT-TERM BORROWINGS - NARRATIVE (Details)	12 Months Ended
	Dec. 31, 2020 USD ($)	Mar. 26, 2020 USD ($)
Unsecured debt | South Jersey Industries Inc. | Unsecured Term Loan
Line of Credit Facility [Line Items]
Amount of facility	$ 150,000,000	$ 150,000,000.0
Unsecured debt | South Jersey Gas Company | South Jersey Gas commercial paper program
Line of Credit Facility [Line Items]
Amount of facility	$ 200,000,000.0
Fixed maturities of notes, which may not exceed specified number of days	270 days
Line of Credit
Line of Credit Facility [Line Items]
Amount of facility	$ 1,060,000,000
Debt covenant, ratio of indebtedness to total capitalization, syndicate	0.70
Line of Credit | South Jersey Industries Inc.
Line of Credit Facility [Line Items]
Amount of facility	$ 650,000,000
Line of Credit | South Jersey Industries Inc. | Line of Credit
Line of Credit Facility [Line Items]
Amount of facility	500,000,000.0
Maximum aggregate letters of credit allowed	200,000,000.0
Increase in maximum aggregate facility subject to certain conditions	100,000,000.0
Maximum aggregate facility, including increase subject to certain conditions	$ 600,000,000.0
Line of Credit | South Jersey Industries Inc. | Revolving Credit Facility
Line of Credit Facility [Line Items]
Term of agreement (in years)	5 years
Line of Credit | South Jersey Industries Inc. | Swingline Loan
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity	$ 50,000,000.0
Line of Credit | SJIU and ETG | Revolving Credit Facility
Line of Credit Facility [Line Items]
Amount of facility	200,000,000.0
Additional aggregate borrowing capacity	200,000,000.0
Maximum aggregate letters of credit allowed	50,000,000.0
Increase in maximum aggregate facility subject to certain conditions	50,000,000.0
Maximum aggregate facility, including increase subject to certain conditions	250,000,000.0
Line of Credit | SJIU and ETG | Swingline Loan
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity	20,000,000.0
Line of Credit | South Jersey Gas Company
Line of Credit Facility [Line Items]
Amount of facility	210,000,000
Line of Credit | South Jersey Gas Company | Revolving Credit Facility
Line of Credit Facility [Line Items]
Amount of facility	$ 200,000,000.0