DERIVATIVE INSTRUMENTS - INCOME STATEMENT RELATED DISCLOSURES (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	$ 1,305	$ (42,925)	$ (9,084)	$ (90,457)
Interest rate contracts | Interest Expense | Home Services and Other
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(62)	121	(185)	121
Energy Services | Physical commodity contracts | Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	171	(11,952)	(1,361)	(10,742)
Energy Services | Physical commodity contracts | Gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	3,306	(44,646)	(2,126)	(67,343)
Energy Services | Financial commodity contracts | Gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(2,231)	13,767	(5,187)	(12,230)
Energy Services | Foreign currency contracts | Gas purchases
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	121	(215)	(225)	(263)
Natural Gas Distribution
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	279	6,887	7,652	(8,964)
Natural Gas Distribution | Physical commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	1,436	(12,879)	4,413	(15,855)
Natural Gas Distribution | Financial commodity contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	(1,157)	7,232	3,239	(1,576)
Natural Gas Distribution | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (losses) gains recognized in income on derivatives	$ 0	$ 12,534	$ 0	$ 8,467