FAIR VALUE - ADDITIONAL INFORMATION (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
NJNG
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Natural gas meter sale leasebacks	$ 31.6	$ 31.4
Level 2 \| NJNG
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Natural gas meter sale leasebacks	26.7	20.9
Solar Asset Financing \| CEV
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	283.0	278.4
Solar Asset Financing \| Fair market value \| CEV
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 290.4	$ 268.1

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant