Restructuring Costs - Changes in Restructuring Reserves (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Restructuring Reserve [Roll Forward]
Beginning balance	$ 6	$ 10
Activity during the period:
Charges	4	8
Cash payments	(8)	(8)
Other	1	(3)
Ending balance	3	7
Less: non-current restructuring reserves	(1)	0
Restructuring reserves – current	2	7
Employee Termination Benefits
Restructuring Reserve [Roll Forward]
Beginning balance	5	10
Activity during the period:
Charges	1	6
Cash payments	(4)	(8)
Other	1	(1)
Ending balance	3	7
Less: non-current restructuring reserves	(1)	0
Restructuring reserves – current	2	7
Plant Shutdown & Other
Restructuring Reserve [Roll Forward]
Beginning balance	1	0
Activity during the period:
Charges	3	2
Cash payments	(4)	0
Other	0	(2)
Ending balance	0	0
Less: non-current restructuring reserves	0	0
Restructuring reserves – current	$ 0	$ 0