LINES OF CREDIT AND SHORT-TERM BORROWINGS - Schedule of Lines of Credit (Details) - USD ($)	Sep. 30, 2021	Sep. 01, 2021
Line of Credit
Line of Credit Facility [Line Items]
Total Facility	$ 1,000,000,000
Usage	155,200,000
Available Liquidity	844,800,000
SJI | Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Total Facility	500,000,000
Usage	61,300,000
Available Liquidity	438,700,000
Letters of credit outstanding	9,800,000
SJI | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility		$ 500,000,000
SJG | Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding	1,900,000
SJG | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility		200,000,000
SJG | Commercial Paper and Letters of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility	250,000,000
Usage	82,900,000
Available Liquidity	167,100,000
ETG | Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding	1,000,000
ETG | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility	250,000,000	$ 200,000,000
Usage	11,000,000
Available Liquidity	$ 239,000,000