Benefit Plans - Change in Benefit Obligation, Change in Fair Value of Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Amounts recognized in the Consolidated Balance Sheets at September 30:
Long-term Employee Benefit Obligations	$ (1,133)	$ (1,009)
Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning obligation	2,366	2,076
Service cost	77	71	$ 84
Interest cost	87	93	87
Plan amendments	(2)	(1)
Benefits paid	(138)	(142)
Benefit obligations assumed in acquisition	67	0
Actuarial loss (gain)	49	318
Settlements	0	(7)
Other, includes translation	(81)	(42)
Ending obligation	2,426	2,366	2,076
Change in fair value of plan assets:
Beginning fair value	1,829	1,785
Actual return on plan assets	(21)	119
Employer contribution	65	104
Benefits paid	(138)	(142)
Plan assets acquired in acquisition	54	0
Settlements	0	(7)
Other, includes translation	(58)	(29)
Ending fair value	1,732	1,829	1,785
Funded Status at September 30:
Unfunded benefit obligation	(694)	(537)
Amounts recognized in the Consolidated Balance Sheets at September 30:
Other	7	3
Salaries, wages and related items	(10)	(8)
Long-term Employee Benefit Obligations	(691)	(531)
Net amount recognized	(694)	(537)
Amounts recognized in Accumulated other comprehensive income (loss) before income taxes at September 30:
Net transition asset	0	0
Prior service credit	103	119
Net actuarial loss	(1,124)	(1,030)
Net amount recognized	(1,021)	(911)
Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning obligation	201	243
Service cost	3	3	6
Interest cost	7	9	10
Plan amendments	0	(37)
Benefits paid	(18)	(24)
Benefit obligations assumed in acquisition	0	0
Actuarial loss (gain)	(11)	0
Settlements	0	0
Other, includes translation	3	6
Ending obligation	186	201	$ 243
Change in fair value of plan assets:
Benefits paid	(18)	(24)
Funded Status at September 30:
Unfunded benefit obligation	(186)	(201)
Amounts recognized in the Consolidated Balance Sheets at September 30:
Other	0	0
Salaries, wages and related items	(15)	(16)
Long-term Employee Benefit Obligations	(171)	(184)
Net amount recognized	(186)	(201)
Amounts recognized in Accumulated other comprehensive income (loss) before income taxes at September 30:
Net transition asset	0	0
Prior service credit	37	42
Net actuarial loss	(30)	(44)
Net amount recognized	$ 7	$ (2)