Pension Plan and Retirement Benefits - Cost Assumptions (Details)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Postretirement Health Care Benefits
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	3.75%	3.50%	4.25%
Pension Plans Defined Benefit Us [Member]
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	3.63%	3.25%	4.00%
Expected return on plan assets (as a percent)	7.25%	7.50%	7.50%
Rate of compensation increase (as a percent)	2.50%	3.50%	3.50%
Pension Plans Defined Benefit Non Us [Member]
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	2.50%	2.30%	3.70%
Expected return on plan assets (as a percent)	3.30%	2.70%	4.10%