Derivative Instruments - Pre-tax Amount of Gains (Losses) on Forward Exchange Contracts Designated as Hedging Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2024
Designated as Hedging Instrument
Unrealized Gain (Loss) On Foreign Currency Derivative Net Before Tax, Amount
Pre-tax amount of (losses) gains reclassified from accumulated other comprehensive income into the Consolidated Statement of Operations related to derivative forward exchange contracts designated as cash flow hedges	$ (7)	$ 2	$ 17
Forward exchange contracts
Unrealized Gain (Loss) On Foreign Currency Derivative Net Before Tax, Amount
Pre-tax (losses) gains recorded in other comprehensive income related to cash flow hedges	10	7	(21)
Location, Statement of Income, Balance [Axis]: us-gaap:CostOfGoodsAndServicesSold \| Designated as Hedging Instrument
Unrealized Gain (Loss) On Foreign Currency Derivative Net Before Tax, Amount
Pre-tax amount of (losses) gains reclassified from accumulated other comprehensive income into the Consolidated Statement of Operations related to derivative forward exchange contracts designated as cash flow hedges	(4)	7	19
Location, Statement of Income, Balance [Axis]: us-gaap:InterestExpenseNonoperating \| Designated as Hedging Instrument
Unrealized Gain (Loss) On Foreign Currency Derivative Net Before Tax, Amount
Pre-tax amount of (losses) gains reclassified from accumulated other comprehensive income into the Consolidated Statement of Operations related to derivative forward exchange contracts designated as cash flow hedges	(4)	(4)	(4)
Location, Statement of Income, Balance [Axis]: us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax \| Designated as Hedging Instrument
Unrealized Gain (Loss) On Foreign Currency Derivative Net Before Tax, Amount
Pre-tax amount of (losses) gains reclassified from accumulated other comprehensive income into the Consolidated Statement of Operations related to derivative forward exchange contracts designated as cash flow hedges	$ 1	$ (1)	$ 2