Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018
Foreign currency exchange derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset	$ 7	$ 8
Foreign currency exchange derivatives | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Derivative asset	1	2
Foreign currency exchange derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	14
Foreign currency exchange derivatives | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	2	2
Cross-currency interest rate swaps | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Derivative asset	17	13
Equity swaps | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	4	2
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815
Derivatives, Fair Value [Line Items]
Derivative asset	19	17
Derivative liability	1,159	1,175
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Long-term debt
Derivatives, Fair Value [Line Items]
Derivative liability, noncurrent	1,143	1,162
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	2	4
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	0	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	14	11
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	2	2
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	17	13
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 | Equity swaps | 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
Derivatives, Fair Value [Line Items]
Derivative asset	6	6
Derivative liability	4	2
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	5	4
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	1	2
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 | Cross-currency interest rate swaps | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Hedging assets, noncurrent	0	0
Derivatives and Hedging Activities Not Designated as Hedging Instruments under ASC 815 | Equity swaps | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, noncurrent	$ 4	$ 2