Income Taxes - Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
U.S. federal and state, Current	$ 2	$ 14	$ 5
U.S. federal and state, Deferred	(30)	114	(26)
U.S. federal and state, Total	(28)	128	(21)
Foreign, Current	95	88	59
Foreign, Deferred	3	(23)	(5)
Foreign, Total	98	65	54
Provision (benefit) for income taxes	$ 70	$ 193	$ 33