Other Operating Income, Net and Other Non-Operating Income (Expense), Net - Other Operating Income, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Component of Operating Income [Abstract]
Finance charges	$ 17	$ 9	$ 17
Gains on sales of fixed assets, net	11	5	3
Gain on early derivative termination	5	0	0
Interest and interest-related income	0	2	6
Utility non-tariff service income	0	0	1
Other, net	0	5	4
Total other operating income, net	$ 33	$ 21	$ 31