Retirement Benefit Plans - Weighted-Average Assumptions Used in Developing Benefit Obligation and Net Pension Expense (Details)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Developing the benefit obligation and the net pension expense for defined benefit pension plans
Discount rate for liabilities	4.10%	3.60%
Discount rate for expenses	3.60%	3.10%
Expected return on assets	7.70%	7.90%