Restructuring and Impairment Costs - Changes in Reserve (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019 USD ($)
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	$ 123
Restructuring reserve ending balance	109
2020 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	7
Utilized—cash	(1)
Utilized—noncash	(1)
Noncash adjustment—underspend	(5)
Restructuring reserve ending balance	5
2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	70
Utilized—cash	(9)
Utilized—noncash	0
Noncash adjustment—underspend	(1)
Restructuring reserve ending balance	60
2018 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	20
Utilized—cash	(5)
Utilized—noncash	0
Noncash adjustment—underspend	(2)
Restructuring reserve ending balance	13
2016 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	27
Utilized—cash	(2)
Utilized—noncash	0
Noncash adjustment—underspend	0
Restructuring reserve ending balance	25
Employee Severance and Termination Benefits | 2020 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	6
Utilized—cash	(1)
Utilized—noncash	0
Restructuring reserve ending balance	5
Employee Severance and Termination Benefits | 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	69
Utilized—cash	(9)
Utilized—noncash	0
Noncash adjustment—underspend	(2)
Restructuring reserve ending balance	58
Employee Severance and Termination Benefits | 2018 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	24
Utilized—cash	(5)
Utilized—noncash	0
Noncash adjustment—underspend	(3)
Restructuring reserve ending balance	16
Employee Severance and Termination Benefits | 2016 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	25
Utilized—cash	(2)
Utilized—noncash	0
Noncash adjustment—underspend	0
Restructuring reserve ending balance	23
Other | 2020 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	1
Utilized—cash	0
Utilized—noncash	0
Restructuring reserve ending balance	1
Other | 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	3
Utilized—cash	0
Utilized—noncash	0
Noncash adjustment—underspend	0
Restructuring reserve ending balance	3
Currency Translation | 2020 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	0
Utilized—cash	0
Utilized—noncash	(1)
Restructuring reserve ending balance	(1)
Currency Translation | 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	(2)
Utilized—cash	0
Utilized—noncash	0
Noncash adjustment—underspend	1
Restructuring reserve ending balance	(1)
Currency Translation | 2018 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	(4)
Utilized—cash	0
Utilized—noncash	0
Noncash adjustment—underspend	1
Restructuring reserve ending balance	(3)
Currency Translation | 2016 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	2
Utilized—cash	0
Utilized—noncash	0
Noncash adjustment—underspend	0
Restructuring reserve ending balance	$ 2