DEBT - Narrative (Details) - Revolving Credit Facility - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Line of Credit Facility [Line Items]
Long-term line of credit, maximum borrowing capacity	$ 1,395,000,000		$ 1,395,000,000
Long-term line of credit	850,000,000		850,000,000
Remaining borrowing capacity	$ 518,000,000		$ 518,000,000
Weighted average interest rate (percent)	5.10%		5.10%
Interest costs capitalized	$ 6,800,000	$ 4,200,000	$ 18,800,000	$ 12,800,000
Revolving Credit Facility, Maturing May 2018
Line of Credit Facility [Line Items]
Long-term line of credit, maximum borrowing capacity	275,000,000		275,000,000
Revolving Credit Facility, Maturing May 2019
Line of Credit Facility [Line Items]
Long-term line of credit, maximum borrowing capacity	$ 1,120,000,000		$ 1,120,000,000