Retirement Plans (Strategic Allocation of Plan Assets) (Details)	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	100.00%
Actual asset allocations
Actual plan asset allocations	100.00%	100.00%	100.00%
Equity Securities [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	20.00%			30.00%
Actual asset allocations
Actual plan asset allocations	21.00%	19.00%	21.00%
Fixed Income Securities [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	80.00%
Fixed Income Funds [Member]
Actual asset allocations
Actual plan asset allocations	78.00%	79.00%	77.00%
Cash and Cash Equivalents [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Actual asset allocations
Actual plan asset allocations	1.00%	2.00%	2.00%
Minimum [Member] | Equity Securities [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	15.00%
Minimum [Member] | Fixed Income Funds [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	75.00%
Minimum [Member] | Cash and Cash Equivalents [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Maximum [Member] | Fixed Income Funds [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	80.00%
Maximum [Member] | Cash and Cash Equivalents [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%