Restructuring Activities - Summary of Severance Reserves and Facility Cost Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost And Reserve [Line Items]
Beginning balance	$ 14	$ 43
Restructuring reserve	1	11
Utilization (cash paid)	(4)	(11)
Ending balance	11	43
Severance Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance	7	36
Restructuring reserve	1	4
Utilization (cash paid)	(3)	(8)
Ending balance	5	32
Facility Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance	7	7
Restructuring reserve	0	7
Utilization (cash paid)	(1)	(3)
Ending balance	$ 6	$ 11