SHAREHOLDERS' EQUITY - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
INCOME (LOSS) BEFORE INCOME TAXES									$ 377	$ 278	$ 381
Tax (benefit) expense	$ (13)	$ (21)	$ (27)	$ (21)	$ (18)	$ (26)	$ (22)	$ (83)	(82)	(149)	(52)
INCOME FROM CONTINUING OPERATIONS									295	129	329
NET INCOME	$ 41	$ 89	$ 74	$ 92	$ 33	$ 67	$ 60	$ (34)	296	126	328
Amount Reclassified from Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
NET INCOME									4	16	28
Amount Reclassified from Accumulated Other Comprehensive Income | Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service (credits) costs									(35)	(35)	(5)
Amortization of actuarial losses									39	46	45
Recognized prior service costs and actuarial losses due to settlement										6
INCOME (LOSS) BEFORE INCOME TAXES									4	17	40
Tax (benefit) expense									0	(1)	(12)
INCOME FROM CONTINUING OPERATIONS									$ 4	$ 16	$ 28