Restructuring Activities - Summary of Severance Reserves and Facility Cost Reserves (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Restructuring Cost And Reserve [Line Items]
Beginning balance	$ 14	$ 43
Restructuring reserve	1	15
Utilization (cash paid)	(9)	(36)
Ending balance	6	22
Severance Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance	7	36
Restructuring reserve	1	7
Utilization (cash paid)	(8)	(29)
Ending balance	0	14
Facility Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance	7	7
Restructuring reserve	0	8
Utilization (cash paid)	(1)	(7)
Ending balance	6	$ 8
Fiscal 2020 Restructuring Severance Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance	0
Restructuring reserve	30
Utilization (cash paid)	(8)
Ending balance	$ 22