Derivative Instruments and Hedging Activities - Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Foreign currency exchange derivatives \| Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset	$ 9	$ 8
Foreign currency exchange derivatives \| Other noncurrent assets
Derivatives, Fair Value [Line Items]
Derivative asset	0	2
Foreign currency exchange derivatives \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	14	11
Foreign currency exchange derivatives \| Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	1	2
Cross-currency interest rate swaps \| Other current assets
Derivatives, Fair Value [Line Items]
Hedging assets, current	20
Cross-currency interest rate swaps \| Other noncurrent assets
Derivatives, Fair Value [Line Items]
Hedging assets, current		13
Equity swaps \| Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Derivative liability		2
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815
Derivatives, Fair Value [Line Items]
Derivative asset	26	17
Derivative liability	1,137	1,175
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 \| Long-term debt
Derivatives, Fair Value [Line Items]
Derivative liability, noncurrent	1,123	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	6	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	13	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	1	2
Derivatives and Hedging Activities Designated as Hedging Instruments under ASC 815 \| Cross-currency interest rate swaps \| Other current assets
Derivatives, Fair Value [Line Items]
Hedging assets, current	20	0
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	0	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	3	6
Derivative liability	1	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	3	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	0	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	1	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 current assets
Derivatives, Fair Value [Line Items]
Hedging assets, 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
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	$ 0	$ 2

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Carrying amount as of the balance sheet date of the asset arising from a financial instrument or a contract used to mitigate a specified risk (hedge), and which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer.

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Carrying amount as of the balance sheet date of the asset arising from a financial instrument or a contract used to hedge price changes in underlying assets, and which are expected to be converted into cash or otherwise disposed of after a year or beyond the normal operating cycle, if longer.

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