Restructuring and Impairment Costs - Changes in Reserve (Details) $ in Millions	3 Months Ended
	Dec. 31, 2018 USD ($)
Restructuring Reserve [Roll Forward]
Restructuring Reserve	$ 141
Restructuring Reserve	150
2018 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	48
Utilized—cash	(9)
Utilized—noncash	(1)
Restructuring Reserve	38
2016 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	75
Utilized—cash	(2)
Restructuring Reserve	73
Employee Severance and Termination Benefits | 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	25
Utilized—cash	(2)
Restructuring Reserve	23
Employee Severance and Termination Benefits | 2018 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	49
Utilized—cash	(9)
Utilized—noncash	0
Restructuring Reserve	40
Employee Severance and Termination Benefits | 2017 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	12
Utilized—cash	(1)
Restructuring Reserve	11
Employee Severance and Termination Benefits | 2016 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	71
Utilized—cash	(2)
Restructuring Reserve	69
Other | 2018 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	1
Utilized—cash	0
Utilized—noncash	(1)
Restructuring Reserve	0
Currency Translation | 2018 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	(2)
Utilized—cash	0
Utilized—noncash	0
Restructuring Reserve	(2)
Currency Translation | 2016 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring Reserve	4
Utilized—cash	0
Restructuring Reserve	$ 4