Income Taxes - Provisions for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Current expense (benefit):
Federal	$ (48)	$ (85)	$ 52
State	7	4	14
Foreign	85	70	70
Total current (benefit) expense	44	(11)	136
Deferred expense (benefit):
Federal	168	135	3
State	48	19	4
Foreign	262	(8)	(50)
Total deferred expense (benefit)	478	146	(43)
Total income tax expense	$ 522	$ 135	$ 93