Debt - Summary of Interest Costs and Payments (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Debt Disclosure [Abstract]
Charged to operations	$ 371	$ 135	$ 138
Capitalized	30	32	33
Total interest costs	401	167	171
Interest paid, net of amounts capitalized	$ 313	$ 135	$ 143