DERIVATIVE INSTRUMENTS - INCOME STATEMENT RELATED DISCLOSURES (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	$ (10,389)	$ (47,532)
Interest rate contracts | Interest Expense | Home Services and Other
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(123)	0
Energy Services | Physical commodity contracts | Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(1,532)	1,210
Energy Services | Physical commodity contracts | Gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(5,432)	(22,697)
Energy Services | Financial commodity contracts | Gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(2,956)	(25,997)
Energy Services | Foreign currency contracts | Gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(346)	(48)
Natural Gas Distribution
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	7,373	(15,851)
Natural Gas Distribution | Physical commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	2,977	(2,976)
Natural Gas Distribution | Financial commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	4,396	(8,808)
Natural Gas Distribution | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	$ 0	$ (4,067)