Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - 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]
Current year actuarial loss (gain)	$ (183)	$ 106	$ 122
Amortization of prior service credit	(32)	(10)	$ 1
Pension Benefits | U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	(113)	30
Amortization of actuarial (loss) gain	(30)	(20)
Current year prior service credit	0	0
Amortization of prior service credit	0	9
Total recognized in other comprehensive income	(143)	19
Total recognized in net periodic benefit cost and other comprehensive income	(147)	14
Pension Benefits | Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	(53)	66
Amortization of actuarial (loss) gain	(2)	0
Current year prior service credit	0	0
Amortization of prior service credit	0	0
Total recognized in other comprehensive income	(55)	66
Total recognized in net periodic benefit cost and other comprehensive income	(52)	66
Other Postretirement Benefits | U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	0	(2)
Amortization of actuarial (loss) gain	2	2
Current year prior service credit	0	0
Amortization of prior service credit	2	3
Total recognized in other comprehensive income	4	3
Total recognized in net periodic benefit cost and other comprehensive income	$ 1	$ (1)