Restructuring and Impairment Costs - Changes in Reserve (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Sep. 30, 2020
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	$ 115
Noncash adjustment—underspend/other			$ 20
Restructuring reserve ending balance	86	$ 115
2022 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	3
Utilized—cash	(1)
Noncash adjustment—underspend/other	6
Restructuring reserve ending balance	2	3
2021 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	22
Utilized—cash	(10)
Noncash adjustment—underspend/other	(1)	16
Restructuring reserve ending balance	11	22
2020 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	77
Utilized—cash	(10)
Noncash adjustment—underspend/other	(6)
Restructuring reserve ending balance	61	77
2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	9
Utilized—cash	(2)
Noncash adjustment—underspend/other	(1)
Restructuring reserve ending balance	6	9
Employee Severance and Termination Benefits | 2022 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	3
Utilized—cash	(1)
Restructuring reserve ending balance	2	3
Employee Severance and Termination Benefits | 2021 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	22
Utilized—cash	(10)
Noncash adjustment—underspend/other	(1)
Restructuring reserve ending balance	11	22
Employee Severance and Termination Benefits | 2020 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	75
Utilized—cash	(10)
Noncash adjustment—underspend/other	(5)
Restructuring reserve ending balance	60	75
Employee Severance and Termination Benefits | 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	8
Utilized—cash	(2)
Noncash adjustment—underspend/other	(1)
Restructuring reserve ending balance	5	8
Currency Translation | 2020 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	2
Utilized—cash	0
Noncash adjustment—underspend/other	(1)
Restructuring reserve ending balance	1	2
Currency Translation | 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	1
Utilized—cash	0
Noncash adjustment—underspend/other	0
Restructuring reserve ending balance	$ 1	$ 1