Income Taxes - Reconciliation Using U.S. Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Computed tax expense at the federal statutory rate	$ 29	$ 105	$ 67
Impact of taxation at different rates, repatriation, losses and other	6	(75)	(37)
Impact of increase (decrease) in valuation allowance on deferred taxes	(16)	(7)	7
Impact of foreign losses for which a current tax benefit is not available		1
Impact of non-deductible net currency losses	2		2
Impact of the Tax Cuts and Jobs Act of 2017	159
U.S. and state benefits from research and experimentation activities	(2)	(2)	(2)
Provision (settlement) of unrecognized tax benefits	1	7	1
Benefit from prior currency loss			(3)
Impact of goodwill impairment charge	18
Permanent differences, net	(1)	5
State taxes, net of federal effect	(3)	(1)	(2)
Provision (benefit) for income taxes	$ 193	$ 33	$ 33