Other Operating Income, Net and Other Non-Operating (Expense) Income, Net - Other Non-Operating Income (Expense), Net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Other Income and Expenses [Abstract]
(Losses) gains on foreign currency contracts, net	$ (20)	$ 38	$ 16
Pension and other postretirement plans non-service expense	0	1	0
Total other non-operating (expense) income, net	$ (20)	$ 39	$ 16