Benefit Plans - Change in Benefit Obligation, Change in Fair Value of Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Amounts recognized in the Consolidated Balance Sheets at September 30:
Long-term Employee Benefit Obligations	$ (1,168)	$ (1,319)
Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning obligation	2,719	2,426
Service cost	110	81	$ 77
Interest cost	61	72	87
Plan amendments	1	0
Benefits paid	(123)	(116)
Impact of divestitures	(19)	0
Actuarial (gain) loss	(134)	302
Settlements	(1)	(15)
Other, includes translation	(36)	30
Ending obligation	2,647	2,719	2,426
Change in fair value of plan assets:
Beginning fair value	1,855	1,732
Actual return on plan assets	134	131
Employer contribution	54	145
Benefits paid	(123)	(116)
Impact of divestitures	(13)	0
Settlements	(1)	(15)
Other, includes translation	26	(21)
Ending fair value	1,932	1,855	1,732
Funded Status at September 30:
Unfunded benefit obligation	(715)	(864)
Amounts recognized in the Consolidated Balance Sheets at September 30:
Other	9	5
Salaries, wages and related items	(17)	(12)
Long-term Employee Benefit Obligations	(707)	(857)
Net amount recognized	(715)	(864)
Amounts recognized in Accumulated other comprehensive income (loss) before income taxes at September 30:
Prior service credit	74	87
Net actuarial loss	1,065	1,307
Net amount recognized	(991)	(1,221)
Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning obligation	184	186
Service cost	3	3	3
Interest cost	4	5	7
Plan amendments	0	1
Benefits paid	(16)	(17)
Impact of divestitures	0	0
Actuarial (gain) loss	(15)	3
Settlements	0	0
Other, includes translation	(4)	(4)
Ending obligation	165	184	$ 186
Funded Status at September 30:
Unfunded benefit obligation	(165)	(184)
Amounts recognized in the Consolidated Balance Sheets at September 30:
Other	0	0
Salaries, wages and related items	(14)	(15)
Long-term Employee Benefit Obligations	(150)	(169)
Net amount recognized	(165)	(184)
Amounts recognized in Accumulated other comprehensive income (loss) before income taxes at September 30:
Prior service credit	28	33
Net actuarial loss	15	32
Net amount recognized	$ 14	$ 1