Additional Financial Information - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Supplemental Cash Flow Information [Abstract]
Accrued interest paid	$ 34,000,000	$ 31,000,000	$ 88,000,000	$ 87,000,000
Income taxes paid net of refunds	7,000,000	7,000,000	13,000,000	15,000,000
Tax refund	$ 0	$ 0	$ 0	$ 9,000,000