SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - DEMAND FEES (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Demand fees	$ 245.5	$ 206.6	$ 218.8
Energy Services
Demand fees	153.0	126.4	141.0
Natural Gas Distribution
Demand fees	$ 92.5	$ 80.2	$ 77.8
Minimum
Storage and pipeline capacity, contract term	1 year
Maximum
Storage and pipeline capacity, contract term	10 years