Accounting Changes and Error Corrections (Policies)	9 Months Ended
Accounting Changes and Error Corrections (Policies)	Sep. 30, 2025
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements, Policy	Recently Issued Accounting Pronouncements In September 2025, the FASB issued ASU 2025-06, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software. This pronouncement updates the guidance on capitalization of internal-use software, including removing the development stages utilized for evaluation of when certain activities are capital eligible. The ASU instead provides that an entity is required to start capitalizing eligible software development costs when (1) management has authorized and committed to funding the software project and (2) it is probable that the project will be completed and the software will be used to perform the function intended, which is referred to as the “probable-to-complete recognition threshold”. This probable-to-complete threshold includes an evaluation of whether there is significant uncertainty associated with the development activities of the software. The ASU is effective for fiscal years beginning after December 15, 2027. We are currently evaluating the impacts this amendment will have on our internal-use software capitalization policy. In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40). This pronouncement requires disaggregated disclosure of income statement expenses for public business entities. The ASU requires disclosure in tabular format of disaggregation of relevant expense captions presented on the income statement by certain natural expense categories with certain related qualitative disclosures within the notes to the financial statements. The ASU does not change the expense captions an entity presents on the income statement. The ASU is effective for fiscal years beginning after December 15, 2026, and interim reporting periods within annual reporting periods beginning after December 15, 2027, as defined in ASU 2025-01, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40). We are currently evaluating the impacts this amendment will have on our required disclosures. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. This pronouncement enhances required income tax disclosures. The pronouncement will require disclosure of specific categories and reconciling items included in the rate reconciliation, disaggregation between federal, state and local income taxes paid, and disclosure of income taxes paid by jurisdictions over a certain threshold. Additionally, the pronouncement eliminates certain required disclosures related to unrecognized tax benefits. This ASU is effective for annual periods beginning after December 15, 2024, with early adoption permitted, and is to be applied on a prospective basis with retrospective application permitted. We will implement and provide the required disclosures in our Annual Report on Form 10-K for the year ended December 31, 2025. Recently Adopted Accounting Pronouncements In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This pronouncement enhances annual and interim disclosure requirements over reportable segments, primarily through enhanced disclosures about significant segment expenses. Specifically, the pronouncement requires disclosure of significant segment expenses that are regularly provided to the CODM and included within each reported measure of segment profit or loss, disclosure of an amount for other segment items representing the difference between segment revenue and segment expenses already disclosed, disclosure of all required annual disclosures for interim periods and disclosure of title and position of the CODM and how the CODM uses reported measures. The pronouncement also allows for more than one measure of segment profit if the CODM uses more than one measure in assessing segment performance. This pronouncement was effective for annual periods beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. NiSource adopted this pronouncement as of December 31, 2024, with retrospective application and updated its disclosures to include significant expenses regularly provided to the CODM, the CODM's title and how the CODM utilizes reported measures. See Note 16, "Business Segment Information," for further discussion.