Fair Value Measurements - Recurring Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 25	$ 23
Total liabilities	20	15
Other current assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	7	8
Other noncurrent assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	1	2
Other noncurrent assets | Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	17	13
Other current liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	14
Other noncurrent liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	2	2
Other noncurrent liabilities | Equity swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	4	2
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
Quoted Prices in Active Markets (Level 1) | Other current assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Quoted Prices in Active Markets (Level 1) | Other noncurrent assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Quoted Prices in Active Markets (Level 1) | Other noncurrent assets | Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Quoted Prices in Active Markets (Level 1) | Other current liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Quoted Prices in Active Markets (Level 1) | Other noncurrent liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Quoted Prices in Active Markets (Level 1) | Other noncurrent liabilities | Equity swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	25	23
Total liabilities	20	15
Significant Other Observable Inputs (Level 2) | Other current assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	7	8
Significant Other Observable Inputs (Level 2) | Other noncurrent assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	1	2
Significant Other Observable Inputs (Level 2) | Other noncurrent assets | Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	17	13
Significant Other Observable Inputs (Level 2) | Other current liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	14	11
Significant Other Observable Inputs (Level 2) | Other noncurrent liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	2	2
Significant Other Observable Inputs (Level 2) | Other noncurrent liabilities | Equity swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	4	2
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
Significant Unobservable Inputs (Level 3) | Other current assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Significant Unobservable Inputs (Level 3) | Other noncurrent assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Significant Unobservable Inputs (Level 3) | Other noncurrent assets | Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Significant Unobservable Inputs (Level 3) | Other current liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Significant Unobservable Inputs (Level 3) | Other noncurrent liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Significant Unobservable Inputs (Level 3) | Other noncurrent liabilities | Equity swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	$ 0	$ 0