Additional Financial Information - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Supplemental Cash Flow Information [Abstract]
Accrued interest paid	$ 181	$ 171	$ 204
Income taxes paid net of refunds	$ 41	$ 25	$ 22