Restructuring Activities - Summary of Severance Reserves and Facility Cost Reserves (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Restructuring Cost And Reserve [Line Items]
Beginning balance	$ 14	$ 43
Restructuring reserve	0	12
Utilization (cash paid)	(7)	(23)
Ending balance	7	32
Severance Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance	7	36
Restructuring reserve	0	4
Utilization (cash paid)	(6)	(18)
Ending balance	1	22
Facility Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance	7	7
Restructuring reserve	0	8
Utilization (cash paid)	(1)	(5)
Ending balance	6	$ 10
Fiscal 2020 Restructuring Severance Costs [Member]
Restructuring Cost And Reserve [Line Items]
Beginning balance	0
Restructuring reserve	17
Utilization (cash paid)	(1)
Ending balance	$ 16