Pension and Other Postretirement Benefits - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	$ 114	$ (47)	$ (113)
Amortization of actuarial (loss) gain	(7)	(3)	(30)
Current year prior service cost	0	0	0
Total recognized in other comprehensive income	107	(50)	(143)
Total recognized in net periodic benefit cost and other comprehensive income	75	(85)	(147)
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	27	30	(53)
Amortization of actuarial (loss) gain	0	0	(2)
Current year prior service cost	1	0	0
Total recognized in other comprehensive income	28	30	(55)
Total recognized in net periodic benefit cost and other comprehensive income	$ 27	$ 26	$ (52)

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

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Amount, before tax, after reclassification adjustment, of increase (decrease) in accumulated other comprehensive income from gain (loss) of defined benefit plan.

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Amount, before tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, before tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

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