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