RETIREMENT MEDICAL PLANS - Components Of Retiree Medical Expense (Details) - U.S. Retiree Medical Plan - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	3	3	14
Amortization of - Prior service cost (benefit)	(35)	(35)	(5)
Actuarial losses	15	17	15
Net periodic expense (income)	$ (17)	$ (15)	$ 24