Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	$ (16)	$ (183)	$ 106
Amortization of prior service credit	(5)	(32)	(10)
Pension Benefits \| U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	(47)	(113)	30
Amortization of actuarial (loss) gain	(3)	(30)	(20)
Amortization of prior service credit	0	0	9
Total recognized in other comprehensive income	(50)	(143)	19
Total recognized in net periodic benefit cost and other comprehensive income	(85)	(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)	30	(53)	66
Amortization of actuarial (loss) gain	0	(2)	0
Amortization of prior service credit	0	0	0
Total recognized in other comprehensive income	30	(55)	66
Total recognized in net periodic benefit cost and other comprehensive income	$ 26	$ (52)	$ 66

Amount recognized in net periodic benefit cost (credit) and other comprehensive (income) loss.

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