Derivative Instruments and Hedging Activities Location and Fair Values of Derivative Instruments and Hedging Activities (Details) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments [Line Items]
Derivative, amount of hedged ordinary shares	1.4
Gross amount recognized, derivative assets	$ 87	$ 97
Gross amount, derivative liabilities	3,020	2,568
Equity swap
Derivative Instruments [Line Items]
Derivative, Amount of Hedged Item	60
Designated as Hedging Instrument
Derivative Instruments [Line Items]
Gross amount recognized, derivative assets	12	16
Gross amount, derivative liabilities	3,020	2,568
Designated as Hedging Instrument | Other current assets | Foreign currency exchange derivatives
Derivative Instruments [Line Items]
Gross amount recognized, derivative assets	10	16
Designated as Hedging Instrument | Other current assets | Commodity derivatives
Derivative Instruments [Line Items]
Gross amount recognized, derivative assets	2	0
Designated as Hedging Instrument | Other noncurrent assets | Equity swap
Derivative Instruments [Line Items]
Gross amount recognized, derivative assets	0	0
Designated as Hedging Instrument | Other current liabilities | Foreign currency exchange derivatives
Derivative Instruments [Line Items]
Gross amount, derivative liabilities	10	23
Designated as Hedging Instrument | Other current liabilities | Commodity derivatives
Derivative Instruments [Line Items]
Gross amount, derivative liabilities	0	1
Designated as Hedging Instrument | Long-term debt | Foreign Currency Denominated Debt [Member]
Derivative Instruments [Line Items]
Gross amount, derivative liabilities	3,010	2,544
Not Designated as Hedging Instrument
Derivative Instruments [Line Items]
Gross amount recognized, derivative assets	75	81
Gross amount, derivative liabilities	0	0
Not Designated as Hedging Instrument | Other current assets | Foreign currency exchange derivatives
Derivative Instruments [Line Items]
Gross amount recognized, derivative assets	17	19
Not Designated as Hedging Instrument | Other current assets | Commodity derivatives
Derivative Instruments [Line Items]
Gross amount recognized, derivative assets	0	0
Not Designated as Hedging Instrument | Other noncurrent assets | Equity swap
Derivative Instruments [Line Items]
Gross amount recognized, derivative assets	58	62
Not Designated as Hedging Instrument | Other current liabilities | Foreign currency exchange derivatives
Derivative Instruments [Line Items]
Gross amount, derivative liabilities	0	0
Not Designated as Hedging Instrument | Other current liabilities | Commodity derivatives
Derivative Instruments [Line Items]
Gross amount, derivative liabilities	0	0
Not Designated as Hedging Instrument | Long-term debt | Foreign Currency Denominated Debt [Member]
Derivative Instruments [Line Items]
Gross amount, derivative liabilities	$ 0	$ 0