Retirement Benefits - Schedule of Significant Assumptions Used in Determining Net Periodic Benefit Cost (Income) and Benefit Obligations (Details)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
U.S. Plans
Net benefit obligation assumptions
Expected gross health care cost trend rate in 2020	5.50%
U.S. Plans | Pension Benefits
Net periodic benefit cost assumptions
Discount rate	3.90%	3.75%	4.55%
Expected return on plan assets	7.50%	7.50%	7.50%
Compensation increase rate	3.50%	3.50%	3.75%
Net benefit obligation assumptions
Compensation increase rate	3.50%	3.50%
U.S. Plans | Other Postretirement Benefits
Net periodic benefit cost assumptions
Discount rate	3.40%	3.10%	3.85%
Net benefit obligation assumptions
Health care cost trend rate	6.50%	6.50%
Non-US Plan
Net benefit obligation assumptions
Expected gross health care cost trend rate in 2020	5.50%
Non-US Plan | Pension Benefits
Net periodic benefit cost assumptions
Discount rate	2.30%	1.77%	2.67%
Expected return on plan assets	5.19%	5.12%	5.21%
Compensation increase rate	2.99%	2.86%	3.11%
Net benefit obligation assumptions
Compensation increase rate	3.02%	2.99%
Non-US Plan | Other Postretirement Benefits
Net periodic benefit cost assumptions
Discount rate	3.20%	2.80%	3.60%
Net benefit obligation assumptions
Health care cost trend rate	4.50%	4.50%