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EMPLOYEE BENEFIT PLANS, PENSION AND OTHER POSTEMPLOYMENT BENEFIT PLANS, NARRATIVE (Details) | 3 Months Ended | 12 Months Ended
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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 |

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