Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 675	$ 430	$ 168
Other comprehensive income	58	75	25
Ending balance	757	675	430
Foreign Currency Translation Gains (Losses)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(244)	(322)	(358)
Other comprehensive income	56	78	36
Ending balance	(188)	(244)	(322)
Minimum Pension Liability Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(3)	(1)	(2)
Other comprehensive income	2	(2)	1
Ending balance	(1)	(3)	(1)
Deferred Gains (Losses) On Derivative Financial Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0	1	13
Other comprehensive income	0	(1)	(12)
Ending balance	0	0	1
Accumulated Other Comprehensive Loss, net
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(247)	(322)	(347)
Ending balance	$ (189)	$ (247)	$ (322)