DERIVATIVE INSTRUMENTS - INCOME STATEMENT RELATED DISCLOSURES (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	$ 48,153	$ 54,634
Energy Services | Physical commodity contracts | Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	5,252	9,836
Energy Services | Physical commodity contracts | Natural gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(5,054)	(1,410)
Energy Services | Financial commodity contracts | Natural gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	47,755	46,093
Energy Services | Foreign Exchange Contract [Member] | Natural gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	200	115
Natural Gas Distribution
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(3,930)	(248)
Natural Gas Distribution | Physical commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	342	840
Natural Gas Distribution | Financial commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	$ (4,272)	$ (1,088)