Derivatives - Summary Impact of Cross-currency Swaps to AOCI and Consolidated Statements of Operations (Detail) - Cross Currency Swaps [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Derivative Instruments Gain Loss [Line Items]
Gain/(Loss) Recognized in AOCI	$ (13)	$ 30	$ 7
(Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations	$ (6)	$ (6)	$ (5)
Derivative Instrument, Gain (Loss) Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest Expense	Interest Expense	Interest Expense
(Gain)/Loss Recognized in Interest Expense in the Consolidated Statements of Operations (Amount Excluded from Effectiveness Testing)	$ 2	$ 2	$ 2