Restructuring and Impairment Costs - Changes in Reserve (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
2021 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	$ 27
Utilized—cash	(5)
Noncash adjustment—underspend	16
Restructuring reserve , ending balance	22	$ 27
2020 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	169	205
Utilized—cash	(87)	(35)
Utilized—noncash	(5)	(1)
Restructuring reserve , ending balance	77	169	$ 205
2019 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	35	70	105
Utilized—cash	(24)	(30)	(32)
Utilized—noncash		2	(3)
Noncash adjustment—underspend	(2)	(7)
Restructuring reserve , ending balance	9	35	70
Employee Severance and Termination Benefits | 2021 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	27
Utilized—cash	(5)
Restructuring reserve , ending balance	22	27
Employee Severance and Termination Benefits | 2020 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	168	203
Utilized—cash	(87)	(35)
Utilized—noncash	(6)	0
Restructuring reserve , ending balance	75	168	203
Employee Severance and Termination Benefits | 2019 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	32	69	101
Utilized—cash	(24)	(30)	(32)
Utilized—noncash		0	0
Noncash adjustment—underspend	0	(7)
Restructuring reserve , ending balance	8	32	69
Other | 2020 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	0	2
Utilized—cash	0	0
Utilized—noncash	0	(2)
Restructuring reserve , ending balance	0	0	2
Other | 2019 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	3	3	4
Utilized—cash	0	0	0
Utilized—noncash		0	(1)
Noncash adjustment—underspend	(3)	0
Restructuring reserve , ending balance	0	3	3
Currency Translation | 2020 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	1	0
Utilized—cash	0	0
Utilized—noncash	1	1
Restructuring reserve , ending balance	2	1	0
Currency Translation | 2019 restructuring plan
Restructuring Reserve [Roll Forward]
Restructuring reserve , beginning balance	0	(2)	0
Utilized—cash	0	0	0
Utilized—noncash		2	(2)
Noncash adjustment—underspend	1	0
Restructuring reserve , ending balance	$ 1	$ 0	$ (2)