Employee Retirement Plans - Actuarial Assumptions for Domestic Plans (Details)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits
Weighted-average assumptions:
Discount rate – benefit obligations	4.00%	3.80%	4.60%
Discount rate – benefit cost	3.80%	4.60%	4.60%
Expected return on plan assets	7.50%	7.55%	7.75%
Rate of increase in salary levels	3.25%	3.25%	3.25%
Other Postretirement Benefits
Weighted-average assumptions:
Discount rate – benefit obligations	4.00%	3.80%	4.70%
Discount rate – benefit cost	3.80%	4.70%	4.60%
Expected return on plan assets	5.00%	5.00%	5.00%
Rate of increase in salary levels	3.25%	3.25%	3.25%