Pension Plan and Retirement Benefits - Cost Assumptions (Details)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Postretirement Health Care Benefits
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	4.13%	3.75%	3.50%
Pension Plans Defined Benefit Us [Member]
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	4.00%	3.63%	3.25%
Expected return on plan assets (as a percent)	7.25%	7.25%	7.50%
Rate of compensation increase (as a percent)	2.50%	2.50%	3.50%
Pension Plans Defined Benefit Non Us [Member]
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	2.80%	2.50%	2.30%
Expected return on plan assets (as a percent)	3.20%	3.30%	2.70%