Accumulated Other Comprehensive Income (Loss) - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 1,590	$ 1,407
Less: Other comprehensive income (loss) attributable to noncontrolling interests	2
Ending Balance	1,705	1,590
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(342)	(353)
Other comprehensive income (loss) before reclassifications	30	18
Amounts reclassified from AOCI	(2)	(2)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	2	5
Ending Balance	(316)	(342)
Pension and Other Postretirement Benefit Liability Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(18)	(9)
Other comprehensive income (loss) before reclassifications	(3)	(5)
Amounts reclassified from AOCI	2	(4)
Ending Balance	(19)	(18)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(360)	(362)
Other comprehensive income (loss) before reclassifications	27	13
Amounts reclassified from AOCI		(6)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		5
Ending Balance	$ (335)	$ (360)