Derivative Instruments and Hedging Activities - Location and Fair Values of Derivative Instruments and Hedging Activities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014
Derivative Instruments [Line Items]
Derivative assets	$ 307	$ 243	$ 255
Derivative liabilities	1,733	1,813	951
Designated as Hedging Instrument
Derivative Instruments [Line Items]
Derivative assets	74	38	31
Derivative liabilities	1,711	1,802	949
Designated as Hedging Instrument | Other Current Assets | Foreign Currency Exchange Derivatives
Derivative Instruments [Line Items]
Derivative assets	50	21	14
Designated as Hedging Instrument | Other Current Assets | Commodity Derivatives
Derivative Instruments [Line Items]
Derivative assets	0	0	3
Designated as Hedging Instrument | Other Current Assets | Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	2	0	0
Designated as Hedging Instrument | Other Current Assets | Cross-Currency Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	20	15	11
Designated as Hedging Instrument | Other Noncurrent Assets | Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative assets	2	2	3
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	50	22	17
Designated as Hedging Instrument | Other Current Liabilities | Commodity Derivatives
Derivative Instruments [Line Items]
Derivative liabilities	7	3	3
Designated as Hedging Instrument | Other Current Liabilities | Cross-Currency Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative liabilities	0	0	1
Designated as Hedging Instrument | Current Portion of Long-Term Debt | Fixed Rate Debt Swapped to Floating
Derivative Instruments [Line Items]
Derivative liabilities	801	125	125
Designated as Hedging Instrument | Long-Term Debt | Fixed Rate Debt Swapped to Floating
Derivative Instruments [Line Items]
Derivative liabilities	853	1,649	803
Designated as Hedging Instrument | Other Noncurrent Liabilities | Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative liabilities	0	3	0
Not Designated as Hedging Instrument
Derivative Instruments [Line Items]
Derivative assets	233	205	224
Derivative liabilities	22	11	2
Not Designated as Hedging Instrument | Other Current Assets | Foreign Currency Exchange Derivatives
Derivative Instruments [Line Items]
Derivative assets	28	13	6
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	205	192	218
Not Designated as Hedging Instrument | Other Current Liabilities | Foreign Currency Exchange Derivatives
Derivative Instruments [Line Items]
Derivative liabilities	22	11	2
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 | Other Noncurrent Liabilities | Interest Rate Swaps
Derivative Instruments [Line Items]
Derivative liabilities	$ 0	$ 0	$ 0