Fair Value Measurements - Recurring Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	$ 26		$ 14
Total assets	30	$ 23
Derivative liability	1,122		$ 1,100
Total liabilities	5	15
Other current assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	17	8
Other current assets | Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	10	12
Other noncurrent assets | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	1	1
Other noncurrent assets | Interest rate cap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset		1
Other noncurrent assets | Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	2	1
Other current liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	5	12
Other noncurrent liabilities | Foreign currency exchange derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability		3
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 current 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 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 | Interest rate cap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset		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
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	30	23
Total liabilities	5	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	17	8
Significant Other Observable Inputs (Level 2) | Other current assets | Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	10	12
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	1
Significant Other Observable Inputs (Level 2) | Other noncurrent assets | Interest rate cap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset		1
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	2	1
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	5	12
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		3
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 current assets | Cross-currency interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	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 | Interest rate cap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset		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