Income Taxes - Reconciliation Using U.S. Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Computed tax expense at the federal statutory rate	$ 85	$ (7)	$ 53
Foreign impact of taxation at different rates, repatriation, valuation allowance, and other	8	4	17
Global Intangible Low Taxed Income (GILTI)	18	(4)	10
Impact of the Coronavirus Aid, Relief, and Economic Security ("CARES") Act of 2020	10	(10)
Impact of increase (decrease) in valuation allowance on U.S. deferred taxes	(1)	228
U.S. and state benefits from research and experimentation activities	(2)	(2)	(2)
Provision (settlement) of unrecognized tax benefits	1	(7)	(8)
Permanent differences, net	7		1
State taxes, net of federal effect	(3)	(11)	(1)
Provision (benefit) for income taxes	$ 123	$ 191	$ 70