Other Commitments And Contingencies	6 Months Ended
Jun. 30, 2026
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Environmental Matters. Our operations are subject to environmental statutes and regulations related to air quality, water quality, hazardous waste and solid waste. We believe that we are in substantial compliance with the environmental regulations currently applicable to our operations. It is management's continued intent to address environmental issues in cooperation with regulatory authorities in such a manner as to achieve mutually acceptable compliance plans. However, there can be no assurance that fines and penalties will not be incurred. Management expects a majority of environmental assessment and remediation costs and asset retirement costs, further described below, to be recoverable through rates. As of June 30, 2026 and December 31, 2025, we had recorded a liability of $80.2 million and $82.6 million, respectively, to cover environmental remediation at various sites. This liability is included in "Other accruals" and "Other noncurrent liabilities and deferred credits" in the Condensed Consolidated Balance Sheets (unaudited). We recognize costs associated with environmental remediation obligations when the incurrence of such costs is probable and the amounts can be reasonably estimated. The original estimates for remediation activities may differ materially from the amount ultimately expended. The actual future expenditures depend on many factors, including laws and regulations, the nature and extent of impact and the method of remediation. These expenditures are not currently estimable at some sites. We periodically adjust our liability as information is collected and estimates become more refined. CERCLA. Our subsidiaries are potentially responsible parties at waste disposal sites under CERCLA and similar state laws. Under CERCLA, each potentially responsible party can be held jointly, severally and strictly liable for the remediation costs as the EPA, or state, can allow the parties to pay for remedial action or perform remedial action themselves and request reimbursement from the potentially responsible parties. Our affiliates have retained CERCLA environmental liabilities, including remediation liabilities, associated with certain current and former operations. At this time, we cannot estimate the full cost of remediating properties that have not yet been investigated, but it is possible that the future costs could be material to the Condensed Consolidated Financial Statements (unaudited). MGP. We maintain a program to identify and investigate former MGP sites where our subsidiaries or predecessors may have liability. The program has identified 36 such sites where liability is probable. Remedial actions at many of these sites are being overseen by state or federal environmental agencies through consent agreements or voluntary remediation agreements. We utilize a probabilistic model to estimate our future remediation costs related to MGP sites. The model was prepared with the assistance of a third party and incorporates our experience and general industry experience with remediating MGP sites. We perform an annual update of the model in the second quarter each year. No material changes to the estimated future remediation costs were identified during the update completed as of June 30, 2026. Our total estimated liability related to the facilities subject to remediation was $72.6 million and $75.5 million at June 30, 2026 and December 31, 2025, respectively. The liability represents our best estimate of the probable cost to remediate the MGP sites. Remediation costs are estimated based on the best available information, applicable remediation standards at the balance sheet date and experience with similar facilities. CCRs. NIPSCO continues to meet the compliance requirements established by the EPA for the regulation of CCRs. The CCR rule requirements currently in effect required revisions to previously recorded legal obligations associated with the retirement of certain NIPSCO facilities. The actual asset retirement costs related to the CCR rule may vary substantially from the estimates used to record the increased asset retirement obligation due to the uncertainty about the requirements that will be established by environmental authorities, compliance strategies that will be used, and the preliminary nature of available data used to estimate costs. As allowed by the rule, NIPSCO will continue to collect data over time to determine the specific compliance solutions and associated costs and, as a result, the actual costs may vary. In May 2024, the EPA finalized changes to the current CCR regulations ("Legacy CCR Rule"), which address inactive surface impoundments at inactive facilities, referred to as legacy impoundments, and CCR management units ("CCRMUs") at inactive and active facilities. The rule largely requires these newly regulated units to conform to existing requirements, such as groundwater monitoring, closure requirements, and post-closure care. NIPSCO continues to assess whether existing legal obligations associated with the retirement of certain facilities must be revised and to estimate probable additional required asset retirement costs. NIPSCO expects to receive recovery of any such costs through existing and future depreciation rates. Other Matters. EPC Agreements. GenCo has entered into certain EPC contracts to construct generation capacity assets to support our data center strategy, requiring payments at specified periods. In certain instances, we may terminate for convenience the EPC Contracts and pay certain incurred project costs and termination fees. Pool Resource Asset Agreements. As of June 30, 2026, GenCo executed two fixed price ESA contracts to support the contracted customer demand, which are contingent on regulatory approval (such approval being the responsibility of the respective developers). GenCo has committed approximately $658.7 million under these ESAs over 15 years; however, GenCo has exercised an option and intends to convert one of these ESAs, which relates to a battery storage project (the “Tipton BESS Project”) with 167 MW nameplate capacity that is expected to be completed in 2028, to a BTA (the “Tipton BTA”). GenCo also entered into a battery e-storage supply agreement of which approximately $122.7 million is considered a noncancelable commitment as of June 30, 2026. We have provided a guarantee related to this supply agreement under which the total guarantee as of June 30, 2026 is $245.4 million. As of June 30, 2026, NIPSCO entered into market capacity purchase agreements to secure additional capacity for the period 2028 through 2030 for approximately $174.6 million to support the contracted demand load of its data center customers. In April 2026, GenCo entered into a capacity agreement for the period from 2028 through 2040 for approximately $1.1 billion, also to support the contracted demand load of its data center customers. This capacity agreement is subject to regulatory approval.

It is management's continued intent to address environmental issues in cooperation with regulatory authorities in such a manner as to achieve mutually acceptable compliance plans. However, there can be no assurance that fines and penalties will not be incurred. Management expects a majority of environmental assessment and remediation costs and asset retirement costs, further described below, to be recoverable through rates.

As of June 30, 2026 and December 31, 2025, we had recorded a liability of $80.2 million and $82.6 million, respectively, to cover environmental remediation at various sites. This liability is included in "Other accruals" and "Other noncurrent liabilities and deferred credits" in the Condensed Consolidated Balance Sheets (unaudited). We recognize costs associated with environmental remediation obligations when the incurrence of such costs is probable and the amounts can be reasonably estimated. The original estimates for remediation activities may differ materially from the amount ultimately expended. The actual future expenditures depend on many factors, including laws and regulations, the nature and extent of impact and the method of remediation. These expenditures are not currently estimable at some sites. We periodically adjust our liability as information is collected and estimates become more refined.

CERCLA. Our subsidiaries are potentially responsible parties at waste disposal sites under CERCLA and similar state laws. Under CERCLA, each potentially responsible party can be held jointly, severally and strictly liable for the remediation costs as the EPA, or state, can allow the parties to pay for remedial action or perform remedial action themselves and request reimbursement from the potentially responsible parties. Our affiliates have retained CERCLA environmental liabilities, including remediation liabilities, associated with certain current and former operations. At this time, we cannot estimate the full cost of remediating properties that have not yet been investigated, but it is possible that the future costs could be material to the Condensed Consolidated Financial Statements (unaudited).

MGP. We maintain a program to identify and investigate former MGP sites where our subsidiaries or predecessors may have liability. The program has identified 36 such sites where liability is probable. Remedial actions at many of these sites are being overseen by state or federal environmental agencies through consent agreements or voluntary remediation agreements.

We utilize a probabilistic model to estimate our future remediation costs related to MGP sites. The model was prepared with the assistance of a third party and incorporates our experience and general industry experience with remediating MGP sites. We perform an annual update of the model in the second quarter each year. No material changes to the estimated future remediation costs were identified during the update completed as of June 30, 2026. Our total estimated liability related to the facilities subject to remediation was $72.6 million and $75.5 million at June 30, 2026 and December 31, 2025, respectively. The liability represents our best estimate of the probable cost to remediate the MGP sites. Remediation costs are estimated based on the best available information, applicable remediation standards at the balance sheet date and experience with similar facilities.

CCRs. NIPSCO continues to meet the compliance requirements established by the EPA for the regulation of CCRs. The CCR rule requirements currently in effect required revisions to previously recorded legal obligations associated with the retirement of certain NIPSCO facilities. The actual asset retirement costs related to the CCR rule may vary substantially from the estimates used to record the increased asset retirement obligation due to the uncertainty about the requirements that will be established by environmental authorities, compliance strategies that will be used, and the preliminary nature of available data used to estimate costs. As allowed by the rule, NIPSCO will continue to collect data over time to determine the specific compliance solutions and associated costs and, as a result, the actual costs may vary.

In May 2024, the EPA finalized changes to the current CCR regulations ("Legacy CCR Rule"), which address inactive surface impoundments at inactive facilities, referred to as legacy impoundments, and CCR management units ("CCRMUs") at inactive and active facilities. The rule largely requires these newly regulated units to conform to existing requirements, such as groundwater monitoring, closure requirements, and post-closure care. NIPSCO continues to assess whether existing legal obligations associated with the retirement of certain facilities must be revised and to estimate probable additional required asset retirement costs. NIPSCO expects to receive recovery of any such costs through existing and future depreciation rates.

EPC Agreements. GenCo has entered into certain EPC contracts to construct generation capacity assets to support our data center strategy, requiring payments at specified periods. In certain instances, we may terminate for convenience the EPC Contracts and pay certain incurred project costs and termination fees.

Pool Resource Asset Agreements. As of June 30, 2026, GenCo executed two fixed price ESA contracts to support the contracted customer demand, which are contingent on regulatory approval (such approval being the responsibility of the respective developers). GenCo has committed approximately $658.7 million under these ESAs over 15 years; however, GenCo has exercised an option and intends to convert one of these ESAs, which relates to a battery storage project (the “Tipton BESS Project”) with 167 MW nameplate capacity that is expected to be completed in 2028, to a BTA (the “Tipton BTA”).

GenCo also entered into a battery e-storage supply agreement of which approximately $122.7 million is considered a noncancelable commitment as of June 30, 2026. We have provided a guarantee related to this supply agreement under which the total guarantee as of June 30, 2026 is $245.4 million.

As of June 30, 2026, NIPSCO entered into market capacity purchase agreements to secure additional capacity for the period 2028 through 2030 for approximately $174.6 million to support the contracted demand load of its data center customers. In April 2026, GenCo entered into a capacity agreement for the period from 2028 through 2040 for approximately $1.1 billion, also to support the contracted demand load of its data center customers. This capacity agreement is subject to regulatory approval.