RETIREMENT MEDICAL PLANS - Amount Of Retiree Medical Obligations Recorded In Accumulated Other Comprehensive Loss Net Of Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension and other postretirement benefit, tax	$ 147	$ 33	$ 5
U.S. Retiree Medical Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Balance, beginning	96	89
Net actuarial (gain) loss for the year	(8)	27
Recognized prior service costs due to plan amendment	(315)
Amortization for the year	(10)	(12)
Pension and other postretirement benefit, tax	126	(8)
Balance, ending	(111)	96	89
U.S. Retiree Medical Plan | Net Actuarial Loss
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Balance, beginning	107	101
Net actuarial (gain) loss for the year	(8)	27
Recognized prior service costs due to plan amendment	0
Amortization for the year	(15)	(13)
Pension and other postretirement benefit, tax	8	(8)
Balance, ending	92	107	101
U.S. Retiree Medical Plan | Prior Service Cost (Benefit)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Balance, beginning	(11)	(12)
Net actuarial (gain) loss for the year	0	0
Recognized prior service costs due to plan amendment	(315)
Amortization for the year	5	1
Pension and other postretirement benefit, tax	118	0
Balance, ending	$ (203)	$ (11)	$ (12)