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, 2022	Sep. 30, 2021	Sep. 30, 2020
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial (gain) loss	$ 170	$ (143)	$ (5)
Amortization of actuarial gain (loss)	0	(3)	(14)
Total recognized in other comprehensive (income) loss	170	(146)	(19)
Total recognized in net periodic benefit cost and other comprehensive (income) loss	124	(189)	(49)
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial (gain) loss	(5)	(45)	21
Amortization of actuarial gain (loss)	0	(6)	(2)
Total recognized in other comprehensive (income) loss	(5)	(51)	19
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$ (10)	$ (48)	$ 20

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 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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