Financial Instruments and Fair Value Measurements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Sep. 30, 2013
Fair Value Disclosures [Abstract]
Remaining cash equivalents	$ 709		$ 709		$ 1,009
Maturity period of cash equivalents at the time of purchase			Three months or less
Maturity period of instruments in short-term investments			Three months and less than one year
Fair value of long-term debt	4,100		4,100		4,000
Transfer of assets in and out of level 1, 2 and 3 measurements during the period
Transfer of liabilities in and out of level 1, 2 and 3 measurements during the period