Regulation (Tables)

12 Months Ended

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.