Retirement Benefits - Schedule of Weighted Average Allocation Of Plan Assets (Details)	Sep. 30, 2019	Sep. 30, 2018
Equity securities
Asset Allocation
Target Allocations	54.00%
As of the balance sheet date	49.00%	53.00%
Debt securities
Asset Allocation
Target Allocations	39.00%
As of the balance sheet date	44.00%	39.00%
Other
Asset Allocation
Target Allocations	7.00%
As of the balance sheet date	7.00%	8.00%
Minimum | Equity securities
Asset Allocation
Target Allocations	40.00%
Minimum | Debt securities
Asset Allocation
Target Allocations	30.00%
Minimum | Other
Asset Allocation
Target Allocations	0.00%
Maximum | Equity securities
Asset Allocation
Target Allocations	65.00%
Maximum | Debt securities
Asset Allocation
Target Allocations	50.00%
Maximum | Other
Asset Allocation
Target Allocations	15.00%