Retirement Plans - Components and Assumptions of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 7	$ 8	$ 8
Interest cost	13	14	12
Expected return on plan assets	(18)	(18)	(17)
Net actuarial (gain) loss	49	(24)	(43)
Settlement (gain) loss	2	0	0
Net periodic benefit cost (credit)	$ 53	$ (20)	$ (40)
Pension Plan | United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.29%	3.85%	3.70%
Expected return on plan assets	5.00%	5.15%	5.50%
Pension Plan | Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	2.71%	2.62%	2.10%
Expected return on plan assets	4.08%	4.19%	3.80%
Rate of compensation increase	3.46%	3.53%	4.00%
Postretirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	0	0	1
Expected return on plan assets	0	0	0
Net actuarial (gain) loss	0	0	(2)
Settlement (gain) loss	0	(15)	0
Net periodic benefit cost (credit)	$ 0	$ (15)	$ (1)
Discount rate			3.25%
Expected return on plan assets			3.35%