Fair Value Measurements - Fair Value Hierarchy for Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 37	$ 18
Total liabilities	14	41
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Total liabilities	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	37	18
Total liabilities	14	41
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Total liabilities	0	0
Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other current assets	$ 36	$ 15
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]	Other current assets	Other current assets
Other noncurrent assets	$ 1	$ 3
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other noncurrent assets	Other noncurrent assets
Other current liabilities	$ 7	$ 32
Derivative Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other current liabilities	Other current liabilities
Other noncurrent liabilities	$ 3	$ 9
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other noncurrent liabilities	Other noncurrent liabilities
Foreign currency exchange derivatives | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other current assets	$ 0	$ 0
Other noncurrent assets	0	0
Other current liabilities	0	0
Other noncurrent liabilities	0	0
Foreign currency exchange derivatives | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other current assets	36	15
Other noncurrent assets	1	3
Other current liabilities	7	32
Other noncurrent liabilities	3	9
Foreign currency exchange derivatives | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other current assets	0	0
Other noncurrent assets	0	0
Other current liabilities	0	0
Other noncurrent liabilities	0	$ 0
Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other current liabilities	$ 1
Derivative Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other current liabilities
Other noncurrent liabilities	$ 3
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other noncurrent liabilities
Cross-currency interest rate swaps | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other current liabilities	$ 0
Other noncurrent liabilities	0
Cross-currency interest rate swaps | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other current liabilities	1
Other noncurrent liabilities	3
Cross-currency interest rate swaps | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other current liabilities	0
Other noncurrent liabilities	$ 0