SHAREHOLDERS' EQUITY - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	$ (809)	$ (766)	$ (749)
Other comprehensive income (loss) before reclassification	224	(78)	(120)
Amounts reclassified from accumulated other comprehensive loss	40	35	103
Net current-period other comprehensive income (loss)	264	(43)	(17)
Ending balance	(545)	(809)	(766)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(66)	(54)	41
Other comprehensive income (loss) before reclassification	25	(12)	(96)
Amounts reclassified from accumulated other comprehensive loss	0	0	1
Net current-period other comprehensive income (loss)	25	(12)	(95)
Ending balance	(41)	(66)	(54)
Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(740)	(705)	(789)
Other comprehensive income (loss) before reclassification	200	(70)	(18)
Amounts reclassified from accumulated other comprehensive loss	40	35	102
Net current-period other comprehensive income (loss)	240	(35)	84
Ending balance	(500)	(740)	(705)
Unrealized Loss
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(3)	(7)	(1)
Other comprehensive income (loss) before reclassification	(1)	4	(6)
Amounts reclassified from accumulated other comprehensive loss	0	0	0
Net current-period other comprehensive income (loss)	(1)	4	(6)
Ending balance	$ (4)	$ (3)	$ (7)