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Derivatives - Summary Impact of Cross-currency Swaps Net of Tax to AOCI and Consolidated Statements of Operations (Detail) - Cross Currency Swaps [Member] - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Derivative Instruments Gain Loss [Line Items] |  |  |
Gain/(loss) recognized in AOCI | $ (8) | $ (6) | $ (13)
(Gain)/loss reclassified from AOCI into Interest expense | (4) | (4) | (6)
(Gain)/loss recognized in Interest expense (amount excluded from effectiveness testing) | $ 2 | $ 2 | $ 2
Derivative Instrument Gain Loss Reclassified from Aoci into Income Expense Effective Portion Statement of Income or Comprehensive Income [Extensible Enumeration] | Interest Expense, Operating and Nonoperating | Interest Expense, Operating and Nonoperating | Interest Expense, Operating and Nonoperating

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- Definition Derivative instrument gain loss reclassified from Aoci into income expense effective portion statement of income or comprehensive income. + References No definition available. + Details
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- Definition Derivative instruments gain loss reclassified from accumulated oci into interest expense net. + References No definition available. + Details
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- Definition Derivative instruments gain loss recognized in interest expense amount excluded from effectiveness testing net. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. 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