RETIREMENT MEDICAL PLANS - Amount Of Retiree Medical Obligations Recorded In Accumulated Other Comprehensive Loss Net Of Tax (Details) - U.S. Retiree Medical Plan - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Balance, beginning	$ (102)	$ (111)
Net actuarial (gain) loss for the year	4	(5)
Recognized prior service costs due to plan amendment	(15)
Amortization for the year	20	18
Deferred tax impact	(2)	(4)
Balance, ending	(95)	(102)
Net Actuarial Loss
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Balance, beginning	76	92
Net actuarial (gain) loss for the year	4	(5)
Recognized prior service costs due to plan amendment	0
Amortization for the year	(15)	(17)
Deferred tax impact	5	6
Balance, ending	70	76
Prior Service Cost (Benefit)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Balance, beginning	(178)	(203)
Net actuarial (gain) loss for the year	0	0
Recognized prior service costs due to plan amendment	(15)
Amortization for the year	35	35
Deferred tax impact	(7)	(10)
Balance, ending	$ (165)	$ (178)