Income Taxes - Reconciliation of U.S. Federal Statutory Tax Rate to Effective Tax Rate (Details)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Operating Loss Carryforwards [Line Items]
U.S. federal statutory tax rate	21.00%	21.00%	21.00%
Difference in tax rate due to:
Goodwill impairment not deductible for tax	11.60%	(7.30%)	0.00%
State income taxes, net of federal benefit	6.80%	(1.70%)	2.30%
Investment tax credits	(6.80%)	0.50%	0.00%
Valuation allowance adjustments	(6.30%)	1.10%	(0.50%)
Regulated entity depreciation normalization	(4.50%)	0.70%	(0.80%)
Notional interest deduction	(3.80%)	0.70%	(0.90%)
State NOL adjustment upon disposition	2.40%	0.00%	0.00%
Uncertain tax positions	(2.40%)	(0.70%)	0.00%
Impairment of equity investment	2.20%	0.00%	0.00%
Federal refund interest accrual	(1.10%)	0.00%	0.00%
Effects of foreign operations	0.10%	3.10%	5.30%
Other, net	(1.90%)	0.60%	(0.10%)
Effective tax rate	20.90%	18.20%	22.60%
Effects of tax rate changes – State, net of federal benefit
Difference in tax rate due to:
Effects of tax rate changes	3.60%	0.20%	(1.40%)
Effects of tax rate changes - International
Difference in tax rate due to:
Effects of tax rate changes	0.00%	0.00%	(2.30%)