LINES OF CREDIT AND SHORT-TERM BORROWINGS - Narrative (Details)	3 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 26, 2020 USD ($)
Unsecured Debt | South Jersey Gas Commercial Paper Program
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 200,000,000.0
Unsecured Debt | SJI | Unsecured Term Loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 150,000,000.0
Unsecured Debt | SJG | South Jersey Gas Commercial Paper Program
Line of Credit Facility [Line Items]
Fixed maturities of notes, at maximum number of days	270 days
Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 910,000,000
Line of Credit | SJI
Line of Credit Facility [Line Items]
Maximum borrowing capacity	500,000,000
Line of Credit | SJI | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 500,000,000.0
Term (in years)	5 years
Maximum aggregate letters of credit allowed	$ 200,000,000.0
Line of Credit | SJI | Swingline Loan
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity	$ 50,000,000.0
Line of Credit | SJIU and ETG
Line of Credit Facility [Line Items]
Debt covenant, ratio of indebtedness to total capitalization, syndicate	0.70
Line of Credit | SJIU and ETG | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 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 | SJG
Line of Credit Facility [Line Items]
Maximum borrowing capacity	210,000,000
Line of Credit | SJG | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 200,000,000.0