Income Taxes - Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
U.S. federal and state, Current	$ 14	$ 5	$ 7
U.S. federal and state, Deferred	114	(26)	(34)
U.S. federal and state, Total	128	(21)	(27)
Foreign, Current	88	59	62
Foreign, Deferred	(23)	(5)	(2)
Foreign, Total	65	54	60
Provision (benefit) for income taxes	$ 193	$ 33	$ 33