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Income Taxes (Tables) | 12 Months Ended
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Sep. 30, 2025
Income Tax Disclosure [Abstract] |
Schedule of Effective Income Tax Rate Reconciliation | Reconciliations of the provision for income taxes computed at the statutory rate of 21 percent to the reported provisions for income taxes from continuing operations for 2025, 2024, and 2023 are set forth below:
| 2025 |  | 2024 |  | 2023
| (In thousands) |  | % |  | (In thousands) |  | % |  | (In thousands) |  | %
U.S federal statutory tax rate | $ | 310,387 |  |  | 21.0 | % |  | $ | 259,513 |  |  | 21.0 | % |  | $ | 209,925 |  |  | 21.0 | %
State and local income taxes, net of federal income tax effect (1) | 24,254 |  |  | 1.6 | % |  | 27,367 |  |  | 2.2 | % |  | 19,853 |  |  | 2.0 | %
Changes in valuation allowances | — |  |  | — | % |  | 1,106 |  |  | 0.1 | % |  | — |  |  | — | %
Changes in unrecognized tax benefits | 2,004 |  |  | 0.1 | % |  | 926 |  |  | 0.1 | % |  | 5,302 |  |  | 0.5 | %
Nontaxable or nondeductible items | 741 |  |  | 0.1 | % |  | 2,464 |  |  | 0.2 | % |  | 1,000 |  |  | 0.1 | %
Amortization of excess deferred taxes | (60,727) |  |  | (4.1) | % |  | (100,270) |  |  | (8.1) | % |  | (123,953) |  |  | (12.4) | %
Other, net | 2,621 |  |  | 0.2 | % |  | 1,775 |  |  | 0.1 | % |  | 1,652 |  |  | 0.2 | %
Income tax expense | $ | 279,280 |  |  | 18.9 | % |  | $ | 192,881 |  |  | 15.6 | % |  | $ | 113,779 |  |  | 11.4 | %
(1) The states that contribute to the majority (greater than 50%) of the tax effect in this category include Texas and Louisiana.
Schedule of Deferred Tax Assets and Liabilities | The tax effect of temporary differences that gave rise to significant components of the deferred tax liabilities and deferred tax assets at September 30, 2025 and 2024 are presented below:
| 2025 |  | 2024
| (In thousands)
Deferred tax assets: |  |  |
Employee benefit plans | $ | 34,202 |  |  | $ | 41,184 |
Net operating loss carryforwards | 473,642 |  |  | 484,816 |
Charitable and other credit carryforwards | 14,200 |  |  | 12,301 |
Regulatory excess deferred tax | 31,387 |  |  | 46,330 |
Lease asset | 72,973 |  |  | 63,747 |
Other | 31,145 |  |  | 34,934 |
Total deferred tax assets | 657,549 |  |  | 683,312 |
Valuation allowance | (1,365) |  |  | (1,457) |
Net deferred tax assets | 656,184 |  |  | 681,855 |
Deferred tax liabilities: |  |  |
Difference in net book value and net tax value of assets | (3,200,535) |  |  | (2,914,854) |
Gas cost adjustments | (43,819) |  |  | (49,443) |
Winter Storm Uri regulatory asset | (17,993) |  |  | (20,846) |
Lease liability | (66,831) |  |  | (57,177) |
Rate deferral adjustment | (64,640) |  |  | (50,571) |
Interest rate agreements | (135,640) |  |  | (134,536) |
Other | (45,073) |  |  | (47,770) |
Total deferred tax liabilities | (3,574,531) |  |  | (3,275,197) |
Net deferred tax liabilities | $ | (2,918,347) |  |  | $ | (2,593,342) |
Schedule of Unrecognized Tax Benefits | The following table reconciles the beginning and ending balance of our unrecognized tax benefits:
| 2025 |  | 2024 |  | 2023
| (In thousands)
Unrecognized tax benefits - beginning balance | $ | 57,797 |  |  | $ | 58,638 |  |  | $ | 52,683 |
Decrease resulting from prior period tax positions | (1,759) |  |  | (2,867) |  |  | (631) |
Decrease resulting from a lapse in statute of limitations | (5,699) |  |  | (6,188) |  |  | — |
Increase resulting from current period tax positions | 9,993 |  |  | 8,214 |  |  | 6,586 |
Unrecognized tax benefits - ending balance | 60,332 |  |  | 57,797 |  |  | 58,638 |
Less: deferred federal and state income tax benefits | (12,670) |  |  | (12,137) |  |  | (12,314) |
Total unrecognized tax benefits that, if recognized, would impact the effective income tax rate as of the end of the year (1) | $ | 47,662 |  |  | $ | 45,660 |  |  | $ | 46,324 |
(1) As of September 30, 2025, there is an anticipated $43.3 million regulatory offset and associated impact to tax expense to be recorded upon recognition of unrecognized tax benefits.

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