Derivative Instruments and Hedging Activities - Location and Fair Values of Derivative Instruments and Hedging Activities (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015
Derivative Instruments [Line Items]
Derivative assets	$ 172	$ 233	$ 307
Derivative liabilities	1,252	1,727	1,733
Designated as Hedging Instrument
Derivative Instruments [Line Items]
Derivative assets	25	42	74
Derivative liabilities	1,222	1,701	1,711
Designated as Hedging Instrument | Other Current Assets | Foreign Currency Exchange Derivatives
Derivative Instruments [Line Items]
Derivative assets	21	31	50
Designated as Hedging Instrument | Other Current Assets | Commodity Derivatives
Derivative Instruments [Line Items]
Derivative assets	1	0	0
Designated as Hedging Instrument | Other Current Assets | Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	0	1	2
Designated as Hedging Instrument | Other Current Assets | Cross-Currency Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	0	5	20
Designated as Hedging Instrument | Other Noncurrent Assets | Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	3	5	2
Designated as Hedging Instrument | Other Noncurrent Assets | Equity swap
Derivative Instruments [Line Items]
Derivative assets	0	0	0
Designated as Hedging Instrument | Other Current Liabilities | Foreign Currency Exchange Derivatives
Derivative Instruments [Line Items]
Derivative liabilities	30	37	50
Designated as Hedging Instrument | Other Current Liabilities | Commodity Derivatives
Derivative Instruments [Line Items]
Derivative liabilities	3	7	7
Designated as Hedging Instrument | Other Current Liabilities | Cross-Currency Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative liabilities	7	1	0
Designated as Hedging Instrument | Current Portion of Long-Term Debt | Fixed Rate Debt Swapped to Floating
Derivative Instruments [Line Items]
Derivative liabilities	403	801	801
Designated as Hedging Instrument | Long-Term Debt | Fixed Rate Debt Swapped to Floating
Derivative Instruments [Line Items]
Derivative liabilities	450	855	853
Designated as Hedging Instrument | Long-Term Debt | Foreign Currency Denominated Debt [Member]
Derivative Instruments [Line Items]
Derivative liabilities	329	0	0
Not Designated as Hedging Instrument
Derivative Instruments [Line Items]
Derivative assets	147	191	233
Derivative liabilities	30	26	22
Not Designated as Hedging Instrument | Other Current Assets | Foreign Currency Exchange Derivatives
Derivative Instruments [Line Items]
Derivative assets	0	27	28
Not Designated as Hedging Instrument | Other Current Assets | Commodity Derivatives
Derivative Instruments [Line Items]
Derivative assets	0	0	0
Not Designated as Hedging Instrument | Other Current Assets | Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	0	0	0
Not Designated as Hedging Instrument | Other Current Assets | Cross-Currency Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	0	0	0
Not Designated as Hedging Instrument | Other Noncurrent Assets | Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	0	0	0
Not Designated as Hedging Instrument | Other Noncurrent Assets | Equity swap
Derivative Instruments [Line Items]
Derivative assets	147	164	205
Not Designated as Hedging Instrument | Other Current Liabilities | Foreign Currency Exchange Derivatives
Derivative Instruments [Line Items]
Derivative liabilities	30	26	22
Not Designated as Hedging Instrument | Other Current Liabilities | Commodity Derivatives
Derivative Instruments [Line Items]
Derivative liabilities	0	0	0
Not Designated as Hedging Instrument | Other Current Liabilities | Cross-Currency Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative liabilities	0	0	0
Not Designated as Hedging Instrument | Current Portion of Long-Term Debt | Fixed Rate Debt Swapped to Floating
Derivative Instruments [Line Items]
Derivative liabilities	0	0	0
Not Designated as Hedging Instrument | Long-Term Debt | Fixed Rate Debt Swapped to Floating
Derivative Instruments [Line Items]
Derivative liabilities	0	0	0
Not Designated as Hedging Instrument | Long-Term Debt | Foreign Currency Denominated Debt [Member]
Derivative Instruments [Line Items]
Derivative liabilities	$ 0	$ 0	$ 0