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Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		$ 9	$ 1
Prior service (credit) cost	$ 3	(1)
Amortization of prior unrecognized gains (losses)	(3)		1
Net changes recognized in Total other comprehensive (income) loss		8	2
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses			(1)
Amortization of prior unrecognized gains (losses)	1	2	1
Net changes recognized in Total other comprehensive (income) loss	$ 1	2
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		2	(3)
Net changes recognized in Total other comprehensive (income) loss		$ 2	$ (3)

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