Retirement Benefit Plans - Asset Allocation Ranges of Defined Benefit Plan Investments (Details)	Sep. 30, 2019	Sep. 30, 2018
Asset Allocation Range provides flexibility for the Plan's investments
Total	100.00%	100.00%
U.S. equities
Asset Allocation Range provides flexibility for the Plan's investments
Total	51.00%	53.00%
U.S. equities | Minimum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	30.00%
U.S. equities | Maximum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	70.00%
Non-U.S. equities
Asset Allocation Range provides flexibility for the Plan's investments
Total	8.00%	8.00%
Non-U.S. equities | Minimum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	0.00%
Non-U.S. equities | Maximum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	20.00%
U.S. debt securities
Asset Allocation Range provides flexibility for the Plan's investments
Total	39.00%	37.00%
U.S. debt securities | Minimum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	20.00%
U.S. debt securities | Maximum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	70.00%
Non-U.S. debt securities
Asset Allocation Range provides flexibility for the Plan's investments
Total	1.00%	0.00%
Non-U.S. debt securities | Minimum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	0.00%
Non-U.S. debt securities | Maximum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	10.00%
Other securities
Asset Allocation Range provides flexibility for the Plan's investments
Total	1.00%	2.00%
Other securities | Minimum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	0.00%
Other securities | Maximum
Asset Allocation Range provides flexibility for the Plan's investments
Asset allocations	60.00%