Financial Instruments and Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining cash equivalents	$ 838,000,000		$ 1,317,000,000
Fair value of long-term debt	9,400,000,000		11,300,000,000
Fair value of debt reclassified from long term to short term	1,100,000,000		$ 798,000,000
Transfer of assets in and out of level 1, 2 and 3 measurements during the period	0	$ 0
Transfer of liabilities in and out of level 1, 2 and 3 measurements during the period	$ 0	$ 0
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity period of short-term investments at the time of purchase	3 months
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity period of short-term investments at the time of purchase	1 year