Income Taxes - Reconciliation Using U.S. Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Computed tax expense at the federal statutory rate	$ 53	$ 29	$ 105
Impact of taxation at different rates, repatriation, losses and other	42	6	(75)
Impact of increase (decrease) in valuation allowance on deferred taxes	(25)	(16)	(7)
Impact of foreign losses for which a current tax benefit is not available			1
Impact of non-deductible net currency losses		2
Impact of the Tax Cuts and Jobs Act of 2017		159
Global Intangible Low Taxed Income (GILTI)	10
U.S. and state benefits from research and experimentation activities	(2)	(2)	(2)
Provision (settlement) of unrecognized tax benefits	(8)	1	7
Impact of goodwill impairment charge		18
Permanent differences, net	1	(1)	5
State taxes, net of federal effect	(1)	(3)	(1)
Provision (benefit) for income taxes	$ 70	$ 193	$ 33