FINANCIAL INSTRUMENTS (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020 USD ($) counterparty	Jun. 30, 2020 USD ($) counterparty	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of counter parties | counterparty	2	2
Estimated fair value of long-term debt, including current maturities	$ 2,730.0	$ 2,730.0	$ 2,730.0
Net carrying amount	2,680.0	2,680.0	2,540.0
Unamortized debt issuance costs	29.3	29.3	25.5
Debt discount	5.3	5.3	5.3
ETG Utility Operations
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred incremental costs, CARES Act	9.0	9.0
Supplier Concentration Risk | Derivatives Energy Related Assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current and non current derivatives	10.5	$ 10.5
Percentage of current and non current derivatives		24.10%
SJG
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred incremental costs, CARES Act	0.7	$ 0.7
Estimated fair value of long-term debt, including current maturities	982.9	982.9	915.2
Net carrying amount	962.4	962.4	965.1
Unamortized debt issuance costs	8.9	8.9	6.3
SJG | Financing Receivable | Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of loans, net of unamortized discounts	3.1	3.1	3.7
Imputed interest of loans	0.4	0.4	0.5
Loans for upgrading equipment for energy efficiency	38.2	38.2	33.5
Financing Receivable, after Allowance for Credit Loss, Current	5.3	5.3	4.6
Loans for upgrading equipment for energy efficiency, noncurrent	$ 32.9	$ 32.9	$ 28.9
SJG | Financing Receivable | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial term of note (in years)		5 years
SJG | Financing Receivable | Minimum | Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans for upgrading equipment for energy efficiency, term (in years)		2 years
SJG | Financing Receivable | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial term of note (in years)		10 years
SJG | Financing Receivable | Maximum | Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans for upgrading equipment for energy efficiency, term (in years)		10 years