Income Taxes - Provisions for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Current expense (benefit):
Federal	$ (85)	$ 52	$ (2)
State	4	14	26
Foreign	70	70	78
Total current (benefit) expense	(11)	136	102
Deferred expense (benefit):
Federal	135	3	(78)
State	19	4	7
Foreign	(8)	(50)	2
Total deferred expense (benefit)	146	(43)	(69)
Total income tax expense	$ 135	$ 93	$ 33