Income Taxes - Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
U.S. federal and state, Current	$ (1)	$ 2	$ 14
U.S. federal and state, Deferred	139	(30)	114
U.S. federal and state, Total	138	(28)	128
Foreign, Current	62	95	88
Foreign, Deferred	(9)	3	(23)
Foreign, Total	53	98	65
Provision (benefit) for income taxes	$ 191	$ 70	$ 193