Income Taxes - Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
U.S. federal and state, Current	$ 11	$ (1)	$ 2
U.S. federal and state, Deferred	(1)	139	(30)
U.S. federal and state, Total	10	138	(28)
Foreign, Current	103	62	95
Foreign, Deferred	10	(9)	3
Foreign, Total	113	53	98
Provision (benefit) for income taxes	$ 123	$ 191	$ 70