RETIREMENT MEDICAL PLANS - Rollforward Of Retiree Medical Liability (Details) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning of year	$ 1,728,000,000
Actuarial loss (gain)	28,000,000
End of year	1,635,000,000	$ 1,728,000,000
U.S. Retiree Medical Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning of year	445,000,000	436,000,000
Interest cost	14,000,000	18,000,000	$ 19,000,000
Actuarial loss (gain)	(8,000,000)	27,000,000
Plan amendment	(315,000,000)	0
Benefit payments	(32,000,000)	(36,000,000)
End of year	104,000,000	445,000,000	$ 436,000,000
Other	0	2,000,000
Retiree medical liability	$ 104,000,000	$ 447,000,000