Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Sep. 30, 2019 | Dec. 31, 2018 |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset | $ 26 | | $ 14 |
Derivative liability | 1,122 | | $ 1,100 |
Foreign currency exchange derivatives | Other current assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset | 17 | $ 8 | |
Foreign currency exchange derivatives | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset | 1 | 1 | |
Foreign currency exchange derivatives | Other current liabilities | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative liability | 5 | 12 | |
Foreign currency exchange derivatives | Other noncurrent liabilities | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative liability | | 3 | |
Interest rate cap | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset | | 1 | |
Cross-currency interest rate swaps | Other current assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset | 10 | 12 | |
Cross-currency interest rate swaps | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset | 2 | 1 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset | 29 | 19 | |
Derivative liability | 1,126 | 1,109 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Long-term debt | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative liability, noncurrent | 1,121 | 1,094 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Foreign currency exchange derivatives | Other current assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset, current | 16 | 5 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Foreign currency exchange derivatives | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset, noncurrent | 1 | 0 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Foreign currency exchange derivatives | Other current liabilities | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative liability, current | 5 | 12 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Foreign currency exchange derivatives | Other noncurrent liabilities | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative liability, noncurrent | 0 | 3 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Interest rate cap | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset, noncurrent | 0 | 1 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Cross-currency interest rate swaps | Other current assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset, current | 10 | 12 | |
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Cross-currency interest rate swaps | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Hedging assets, noncurrent | 2 | 1 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset | 1 | 4 | |
Derivative liability | 0 | 0 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Long-term debt | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative liability, noncurrent | 0 | 0 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Foreign currency exchange derivatives | Other current assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset, current | 1 | 3 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Foreign currency exchange derivatives | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset, noncurrent | 0 | 1 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Foreign currency exchange derivatives | Other current liabilities | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative liability, current | 0 | 0 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Foreign currency exchange derivatives | Other noncurrent liabilities | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative liability, noncurrent | 0 | 0 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Interest rate cap | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset, noncurrent | 0 | 0 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Cross-currency interest rate swaps | Other current assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Derivative asset, current | 0 | 0 | |
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Cross-currency interest rate swaps | Other noncurrent assets | | | |
Derivatives, Fair Value [Line Items] | | | |
Hedging assets, noncurrent | $ 0 | $ 0 | |