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Regulation (Tables) | 12 Months Ended
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Sep. 30, 2025
Regulated Operations [Abstract] |
Schedule of Regulatory Assets | Significant regulatory assets and liabilities as of September 30, 2025 and 2024 included the following:
| September 30
| 2025 |  | 2024
| (In thousands)
Regulatory assets: |  |  |
Pension and postretirement benefit costs | $ | 262 |  |  | $ | 11,243 |
Infrastructure mechanisms (1) | 314,047 |  |  | 246,734 |
Winter Storm Uri incremental costs | 5,841 |  |  | 10,373 |
Deferred gas costs | 140,626 |  |  | 159,762 |
Regulatory excess deferred taxes (2) | 49,793 |  |  | 51,380 |
Recoverable loss on reacquired debt | 2,903 |  |  | 3,070 |
Deferred pipeline record collection costs | 39,035 |  |  | 41,742 |
System Safety and Integrity Riders (3) | 43,625 |  |  | 38,632 |
Other | 12,597 |  |  | 16,454 |
| $ | 608,729 |  |  | $ | 579,390 |
Regulatory liabilities: |  |  |
Regulatory excess deferred taxes (2) | $ | 190,274 |  |  | $ | 257,001 |
Regulatory cost of removal obligation | 641,019 |  |  | 607,032 |
Deferred gas costs | 6,879 |  |  | 9,142 |
APT annual adjustment mechanism | 99,393 |  |  | 73,119 |
Pension and postretirement benefit costs | 291,351 |  |  | 247,250 |
Other | 40,732 |  |  | 34,338 |
| $ | 1,269,648 |  |  | $ | 1,227,882 |
(1)Infrastructure mechanisms in Texas, Louisiana, and Tennessee allow for the deferral of all eligible expenses associated with capital expenditures incurred pursuant to these rules, including the recording of interest on the deferred expenses until the next rate proceeding (rate case or annual rate filing), at which time investment and costs would be recovered through base rates. (2)Regulatory excess deferred taxes represent changes in our net deferred tax liability related to our cost of service ratemaking due to the enactment of the Tax Cuts and Jobs Act of 2017 (the "TCJA"), a Kansas legislative change enacted in fiscal 2020, and a Louisiana legislative change enacted in fiscal 2025. See Notes 13 and 15 to the consolidated financial statements for further information. (3)In our APT and West Texas Divisions and portions of our Mid-Tex Division, the RRC has approved the deferral of certain system safety and integrity costs incurred in excess of a specified benchmark. These costs are eligible for recovery in a future filing after such costs are approved by the RRC.
Schedule of Regulatory Liabilities | Significant regulatory assets and liabilities as of September 30, 2025 and 2024 included the following:
| September 30
| 2025 |  | 2024
| (In thousands)
Regulatory assets: |  |  |
Pension and postretirement benefit costs | $ | 262 |  |  | $ | 11,243 |
Infrastructure mechanisms (1) | 314,047 |  |  | 246,734 |
Winter Storm Uri incremental costs | 5,841 |  |  | 10,373 |
Deferred gas costs | 140,626 |  |  | 159,762 |
Regulatory excess deferred taxes (2) | 49,793 |  |  | 51,380 |
Recoverable loss on reacquired debt | 2,903 |  |  | 3,070 |
Deferred pipeline record collection costs | 39,035 |  |  | 41,742 |
System Safety and Integrity Riders (3) | 43,625 |  |  | 38,632 |
Other | 12,597 |  |  | 16,454 |
| $ | 608,729 |  |  | $ | 579,390 |
Regulatory liabilities: |  |  |
Regulatory excess deferred taxes (2) | $ | 190,274 |  |  | $ | 257,001 |
Regulatory cost of removal obligation | 641,019 |  |  | 607,032 |
Deferred gas costs | 6,879 |  |  | 9,142 |
APT annual adjustment mechanism | 99,393 |  |  | 73,119 |
Pension and postretirement benefit costs | 291,351 |  |  | 247,250 |
Other | 40,732 |  |  | 34,338 |
| $ | 1,269,648 |  |  | $ | 1,227,882 |
(1)Infrastructure mechanisms in Texas, Louisiana, and Tennessee allow for the deferral of all eligible expenses associated with capital expenditures incurred pursuant to these rules, including the recording of interest on the deferred expenses until the next rate proceeding (rate case or annual rate filing), at which time investment and costs would be recovered through base rates. (2)Regulatory excess deferred taxes represent changes in our net deferred tax liability related to our cost of service ratemaking due to the enactment of the Tax Cuts and Jobs Act of 2017 (the "TCJA"), a Kansas legislative change enacted in fiscal 2020, and a Louisiana legislative change enacted in fiscal 2025. See Notes 13 and 15 to the consolidated financial statements for further information. (3)In our APT and West Texas Divisions and portions of our Mid-Tex Division, the RRC has approved the deferral of certain system safety and integrity costs incurred in excess of a specified benchmark. These costs are eligible for recovery in a future filing after such costs are approved by the RRC.

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- Definition Tabular disclosure of regulatory liabilities. Detailed information about liabilities that result from rate actions of a regulator. Rate actions of a regulator can impose a liability on a regulated enterprise resulting in a regulatory liability. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 405 -Name Accounting Standards Codification -Section 25 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477571/980-405-25-1 + Details
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