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Retirement Plan and Other Post-Retirement Benefits (Tables) | 12 Months Ended
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Sep. 30, 2025
Retirement Benefits [Abstract] |
Schedule of Benefit Obligations, Plan Assets and Funded Status | Reconciliations of the Benefit Obligations, Plan Assets and Funded Status, as well as the components of Net Periodic Benefit Cost and the Weighted Average Assumptions of the Retirement Plan and other post-retirement benefits are shown in the tables below. The components of net periodic benefit cost other than service cost are presented in Other Income (Deductions) on the Consolidated Statements of Income. The date used to measure the Benefit Obligations, Plan Assets and Funded Status is September 30 for fiscal years 2025, 2024 and 2023.
| Retirement Plan |  | Other Post-Retirement Benefits
| Year Ended September 30 |  | Year Ended September 30
| 2025 |  | 2024 |  | 2023 |  | 2025 |  | 2024 |  | 2023
| (Thousands)
Change in Benefit Obligation |  |  |  |  |  |  |  |  |  |  |
Benefit Obligation at Beginning of Period | $ | 822,306 |  | $ | 768,750 |  | $ | 813,828 |  | $ | 321,025 |  | $ | 274,278 |  | $ | 299,283
Service Cost | 4,092 |  | 4,197 |  | 5,187 |  | 519 |  | 434 |  | 587
Interest Cost | 36,892 |  | 43,558 |  | 42,516 |  | 14,501 |  | 15,561 |  | 15,648
Plan Participants’ Contributions | — |  | — |  | — |  | 3,597 |  | 3,401 |  | 3,297
Retiree Drug Subsidy Receipts | — |  | — |  | — |  | 1,514 |  | 1,208 |  | 2,969
Actuarial (Gain) Loss | (17,232) |  | 72,016 |  | (27,313) |  | 17,072 |  | 54,443 |  | (20,789)
Benefits Paid | (66,395) |  | (66,215) |  | (65,468) |  | (27,644) |  | (28,300) |  | (26,717)
Benefit Obligation at End of Period | $ | 779,663 |  | $ | 822,306 |  | $ | 768,750 |  | $ | 330,584 |  | $ | 321,025 |  | $ | 274,278
Change in Plan Assets |  |  |  |  |  |  |  |  |  |  |
Fair Value of Assets at Beginning of Period | $ | 823,985 |  | $ | 784,712 |  | $ | 845,205 |  | $ | 496,065 |  | $ | 455,702 |  | $ | 461,438
Actual Return on Plan Assets | 20,527 |  | 105,488 |  | 4,975 |  | 23,494 |  | 64,783 |  | 17,449
Employer Contributions | — |  | — |  | — |  | 594 |  | 479 |  | 235
Plan Participants’ Contributions | — |  | — |  | — |  | 3,597 |  | 3,401 |  | 3,297
Benefits Paid | (66,395) |  | (66,215) |  | (65,468) |  | (27,644) |  | (28,300) |  | (26,717)
Fair Value of Assets at End of Period | $ | 778,117 |  | $ | 823,985 |  | $ | 784,712 |  | $ | 496,106 |  | $ | 496,065 |  | $ | 455,702
Net Amount Recognized at End of Period (Funded Status) | $ | (1,546) |  | $ | 1,679 |  | $ | 15,962 |  | $ | 165,522 |  | $ | 175,040 |  | $ | 181,424
Amounts Recognized in the Balance Sheets Consist of: |  |  |  |  |  |  |  |  |  |  |
Non-Current Liabilities | $ | (1,546) |  | $ | — |  | $ | — |  | $ | (3,706) |  | $ | (3,511) |  | $ | (2,915)
Non-Current Assets | — |  | 1,679 |  | 15,962 |  | 169,228 |  | 178,551 |  | 184,339
Net Amount Recognized at End of Period | $ | (1,546) |  | $ | 1,679 |  | $ | 15,962 |  | $ | 165,522 |  | $ | 175,040 |  | $ | 181,424
Accumulated Benefit Obligation | $ | 765,747 |  | $ | 804,916 |  | $ | 751,912 |  | N/A |  | N/A |  | N/A
Weighted Average Assumptions Used to Determine Benefit Obligation at September 30 |  |  |  |  |  |  |  |  |  |  |
Discount Rate | 5.28 | % |  | 4.97 | % |  | 5.99 | % |  | 5.30 | % |  | 4.98 | % |  | 5.99 | %
Rate of Compensation Increase | 4.60 | % |  | 4.60 | % |  | 4.60 | % |  | 4.60 | % |  | 4.60 | % |  | 4.60 | %
| Retirement Plan |  | Other Post-Retirement Benefits
| Year Ended September 30 |  | Year Ended September 30
| 2025 |  | 2024 |  | 2023 |  | 2025 |  | 2024 |  | 2023
| (Thousands)
Components of Net Periodic Benefit Cost |  |  |  |  |  |  |  |  |  |  |
Service Cost | $ | 4,092 |  | $ | 4,197 |  | $ | 5,187 |  | $ | 519 |  | $ | 434 |  | $ | 587
Interest Cost | 36,892 |  | 43,558 |  | 42,516 |  | 14,501 |  | 15,561 |  | 15,648
Expected Return on Plan Assets | (58,587) |  | (68,343) |  | (66,593) |  | (26,144) |  | (26,642) |  | (25,612)
Amortization of Prior Service Cost (Credit) | 302 |  | 362 |  | 436 |  | (429) |  | (429) |  | (429)
Recognition of Actuarial (Gain) Loss(1) | 6,481 |  | (1,339) |  | (7,680) |  | 37 |  | (2,266) |  | (8,755)
Net Amortization and Deferral for Regulatory Purposes | (1,375) |  | 16,231 |  | 21,512 |  | (3,857) |  | 8,759 |  | 15,157
Net Periodic Benefit Income | $ | (12,195) |  | $ | (5,334) |  | $ | (4,622) |  | $ | (15,373) |  | $ | (4,583) |  | $ | (3,404)
Weighted Average Assumptions Used to Determine Net Periodic Benefit Cost at September 30 |  |  |  |  |  |  |  |  |  |  |
Effective Discount Rate for Benefit Obligations | 4.97 | % |  | 5.99 | % |  | 5.57 | % |  | 4.98 | % |  | 5.99 | % |  | 5.56 | %
Effective Rate for Interest on Benefit Obligations | 4.68 | % |  | 5.93 | % |  | 5.45 | % |  | 4.69 | % |  | 5.93 | % |  | 5.45 | %
Effective Discount Rate for Service Cost | 5.14 | % |  | 6.01 | % |  | 5.49 | % |  | 5.21 | % |  | 5.99 | % |  | 5.35 | %
Effective Rate for Interest on Service Cost | 4.96 | % |  | 5.98 | % |  | 5.53 | % |  | 5.14 | % |  | 6.01 | % |  | 5.47 | %
Expected Return on Plan Assets | 6.60 | % |  | 7.40 | % |  | 6.90 | % |  | 5.40 | % |  | 6.00 | % |  | 5.70 | %
Rate of Compensation Increase | 4.60 | % |  | 4.60 | % |  | 4.60 | % |  | 4.60 | % |  | 4.60 | % |  | 4.60 | %
(1)Distribution Corporation’s New York jurisdiction calculates the amortization of the actuarial loss on a vintage year basis over 10 years, as mandated by the NYPSC. All the other subsidiaries of the Company utilize the corridor approach.
Schedule of Cumulative Amounts Recognized in Accumulated Other Comprehensive Income (Loss) and Regulatory Assets and Liabilities | The cumulative amounts recognized in accumulated other comprehensive income (loss), regulatory assets, and regulatory liabilities through fiscal 2025, as well as the changes in such amounts during 2025, are presented in the table below:
| Retirement Plan |  | Other Post-Retirement Benefits |  | Non-Qualified Benefit Plans
| (Thousands)
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities(1) |  |  |  |  |
Net Actuarial Loss | $ | (178,675) |  |  | $ | (19,813) |  |  | $ | (13,353) |
Prior Service (Cost) Credit | (1,372) |  |  | 257 |  |  | — |
Net Amount Recognized | $ | (180,047) |  |  | $ | (19,556) |  |  | $ | (13,353) |
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities Recognized During Fiscal 2025(1) |  |  |  |  |
Increase in Actuarial Loss, excluding amortization(2) | $ | (20,828) |  |  | $ | (19,722) |  |  | $ | (1,061) |
Change due to Amortization of Actuarial Loss | 6,481 |  |  | 37 |  |  | 1,101 |
Prior Service (Cost) Credit | 302 |  |  | (429) |  |  | — |
Net Change | $ | (14,045) |  |  | $ | (20,114) |  |  | $ | 40 |
(1)Amounts presented are shown before recognizing deferred taxes. (2)Amounts presented include the impact of actuarial gains/losses related to return on assets, as well as the Actuarial Loss amounts presented in the Change in Benefit Obligation.
Schedule of Expected Benefit Payments | The estimated gross other post-retirement benefit payments and gross amount of Medicare Part D prescription drug subsidy receipts are as follows (dollars in thousands):
| Benefit Payments |  | Subsidy Receipts
2026 | $ | 26,899 |  |  | $ | (1,560) |
2027 | $ | 27,556 |  |  | $ | (1,574) |
2028 | $ | 28,060 |  |  | $ | (1,577) |
2029 | $ | 28,344 |  |  | $ | (1,577) |
2030 | $ | 28,406 |  |  | $ | (1,568) |
2031 through 2035 | $ | 135,297 |  |  | $ | (7,536) |
Schedule of Health Care Cost Trend Rates | Assumed health care cost trend rates as of September 30 were:
| 2025 |  |  | 2024 |  |  | 2023 |
Rate of Medical Cost Increase for Pre Age 65 Participants | 7.25 | % | (1) |  | 6.25 | % | (2) |  | 6.25 | % | (3)
Rate of Medical Cost Increase for Post Age 65 Participants | 5.75 | % | (1) |  | 5.75 | % | (2) |  | 5.00 | % | (3)
Annual Rate of Increase in the Per Capita Cost of Covered Prescription Drug Benefits | 11.75 | % | (1) |  | 10.25 | % | (2) |  | 6.85 | % | (3)
Annual Rate of Increase in the Per Capita Medicare Part B Reimbursement | 5.75 | % | (1) |  | 5.75 | % | (2) |  | 5.00 | % | (3)
Annual Rate of Increase in the Per Capita Medicare Part D Subsidy | 4.00 | % | (1) |  | 4.00 | % | (2) |  | 6.60 | % | (3)
(1)It was assumed that this rate would gradually decline to 4% by 2050. (2)It was assumed that this rate would gradually decline to 4% by 2049. (3)It was assumed that this rate would gradually decline to 4% by 2048.
Schedule of Fair Value of Plan Assets | Below is a listing of the major categories of plan assets held as of September 30, 2025 and 2024, as well as the associated level within the fair value hierarchy in which the fair value measurements in their entirety fall, based on the lowest level input that is significant to the fair value measurement in its entirety (dollars in thousands):
| At September 30, 2025
| Total Fair Value |  | Level 1 |  | Level 2 |  | Level 3 |  | Measured at NAV(6)
Retirement Plan Investments |  |  |  |  |  |  |  |  |
Domestic Equities(1) | $ | 116 |  |  | $ | 116 |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Global Equities(2) | 79,470 |  |  | — |  |  | — |  |  | — |  |  | 79,470 |
Domestic Fixed Income(3)(7) | 645,955 |  |  | — |  |  | 596,905 |  |  | — |  |  | 49,050 |
International Fixed Income(4) | 9,609 |  |  | — |  |  | 9,609 |  |  | — |  |  | — |
Real Estate (5) | 102,373 |  |  | — |  |  | — |  |  | — |  |  | 102,373 |
Cash Held in Collective Trust Funds | 34,077 |  |  | — |  |  | — |  |  | — |  |  | 34,077 |
Total Retirement Plan Investments | 871,600 |  |  | 116 |  |  | 606,514 |  |  | — |  |  | 264,970 |
401(h) Investments | (86,093) |  |  | (12) |  |  | (60,379) |  |  | — |  |  | (25,702) |
Total Retirement Plan Investments (excluding 401(h) Investments) | $ | 785,507 |  |  | $ | 104 |  |  | $ | 546,135 |  |  | $ | — |  |  | $ | 239,268 |
Miscellaneous Accruals, Interest Receivables, and Non-Interest Cash | (7,390) |  |  |  |  |  |  |  |  |
Total Retirement Plan Assets | $ | 778,117 |  |  |  |  |  |  |  |  |
| At September 30, 2024
| Total Fair Value |  | Level 1 |  | Level 2 |  | Level 3 |  | Measured at NAV(6)
Retirement Plan Investments |  |  |  |  |  |  |  |  |
Domestic Equities(1) | $ | 37,984 |  |  | $ | 37,984 |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Global Equities(2) | 38,234 |  |  | — |  |  | — |  |  | — |  |  | 38,234 |
Domestic Fixed Income(3)(7) | 681,755 |  |  | — |  |  | 633,600 |  |  | — |  |  | 48,155 |
International Fixed Income(4) | 8,587 |  |  | — |  |  | 8,587 |  |  | — |  |  | — |
Real Estate (5) | 109,383 |  |  | — |  |  | — |  |  | — |  |  | 109,383 |
Cash Held in Collective Trust Funds | 41,709 |  |  | — |  |  | — |  |  | — |  |  | 41,709 |
Total Retirement Plan Investments | 917,652 |  |  | 37,984 |  |  | 642,187 |  |  | — |  |  | 237,481 |
401(h) Investments | (83,682) |  |  | (3,500) |  |  | (59,166) |  |  | — |  |  | (21,016) |
Total Retirement Plan Investments (excluding 401(h) Investments) | $ | 833,970 |  |  | $ | 34,484 |  |  | $ | 583,021 |  |  | $ | — |  |  | $ | 216,465 |
Miscellaneous Accruals, Interest Receivables, and Non-Interest Cash | (9,985) |  |  |  |  |  |  |  |  |
Total Retirement Plan Assets | $ | 823,985 |  |  |  |  |  |  |  |  |
(1)Domestic Equities include mostly collective trust funds, common stock, and exchange traded funds. (2)Global Equities are comprised of collective trust funds. (3)Domestic Fixed Income securities include mostly collective trust funds, corporate/government bonds and mortgages, and exchange traded funds. (4)International Fixed Income securities are comprised mostly of corporate/government bonds. (5)Real Estate consists of investments held in a collective trust fund and a partnership. (6)Reflects the authoritative guidance related to investments measured at net asset value (NAV). (7)Domestic Fixed Income securities include $6.2 million and $8.5 million of derivative instruments used as part of the Company’s overall liability-driven investment strategy as a way to assist in matching the duration of the assets of the Retirement Plan investments with its liability to plan participants as of September 30, 2025 and September 30, 2024, respectively.
| At September 30, 2025
| Total Fair Value |  | Level 1 |  | Level 2 |  | Level 3 |  | Measured at NAV(1)
Other Post-Retirement Benefit Assets held in VEBA Trusts |  |  |  |  |  |  |  |  |
Collective Trust Funds — Global Equities | $ | 232,395 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 232,395 |
Exchange Traded Funds — Fixed Income | 165,601 |  |  | 165,601 |  |  | — |  |  | — |  |  | — |
Cash Held in Collective Trust Funds | 12,302 |  |  | — |  |  | — |  |  | — |  |  | 12,302 |
Total VEBA Trust Investments | 410,298 |  |  | 165,601 |  |  | — |  |  | — |  |  | 244,697 |
401(h) Investments | 86,093 |  |  | 12 |  |  | 60,379 |  |  | — |  |  | 25,702 |
Total Investments (including 401(h) Investments) | $ | 496,391 |  |  | $ | 165,613 |  |  | $ | 60,379 |  |  | $ | — |  |  | $ | 270,399 |
Miscellaneous Accruals (including Current and Deferred Taxes, Claims Incurred But Not Reported, Administrative) | (285) |  |  |  |  |  |  |  |  |
Total Other Post-Retirement Benefit Assets | $ | 496,106 |  |  |  |  |  |  |  |  |
| At September 30, 2024
| Total Fair Value |  | Level 1 |  | Level 2 |  | Level 3 |  | Measured at NAV(1)
Other Post-Retirement Benefit Assets held in VEBA Trusts |  |  |  |  |  |  |  |  |
Collective Trust Funds — Global Equities | $ | 82,814 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 82,814 |
Exchange Traded Funds — Fixed Income | 314,052 |  |  | 314,052 |  |  | — |  |  | — |  |  | — |
Cash Held in Collective Trust Funds | 14,274 |  |  | — |  |  | — |  |  | — |  |  | 14,274 |
Total VEBA Trust Investments | 411,140 |  |  | 314,052 |  |  | — |  |  | — |  |  | 97,088 |
401(h) Investments | 83,682 |  |  | 3,500 |  |  | 59,166 |  |  | — |  |  | 21,016 |
Total Investments (including 401(h) Investments) | $ | 494,822 |  |  | $ | 317,552 |  |  | $ | 59,166 |  |  | $ | — |  |  | $ | 118,104 |
Miscellaneous Accruals (Including Current and Deferred Taxes, Claims Incurred But Not Reported, Administrative) | 1,243 |  |  |  |  |  |  |  |  |
Total Other Post-Retirement Benefit Assets | $ | 496,065 |  |  |  |  |  |  |  |  |
(1)Reflects the authoritative guidance related to investments measured at net asset value (NAV).

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