EMPLOYEE BENEFIT PLANS, PENSION AND OTHER POSTEMPLOYMENT BENEFIT PLANS, NARRATIVE (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2016 USD ($) plan	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of noncontributory defined benefit retirement plans (in plans) | plan		2
Required number of years of service (more than)		1 year
Years of service and average compensation, basis period for plan benefits		60 months
Employer contributions	$ 30,000,000		$ 0
Long-term real rate of return on assets (as a percent)		5.00%
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions		$ 3,235,000	5,672,000	$ 5,000,000
OPEB | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated future employer contributions over the next five years		3,000,000
OPEB | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated future employer contributions over the next five years		$ 5,000,000
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer discretionary contributions			$ 0