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Business Segment Information (Schedule Of Operating Income Derived From Revenues And Expenses By Segment) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2024
Segment Reporting Information [Line Items] |  |  |  |  |
Consolidated Operating Income (Loss) | $ 297.5 | $ 218.3 | $ 1,319.8 | $ 1,038.7 |
Total Assets | 34,402.9 |  | 34,402.9 |  | $ 31,788.1
Regulated Operating Revenue | 1,273.1 | 1,076.3 | 4,739.3 | 3,867.3 |
Cost of energy | 193.6 | 165.9 | 1,102.9 | 755.6 |
Utilities Operating Expense, Maintenance and Operations | 401.1 | 357.4 | 1,225.1 | 1,093.5 |
Taxes, Miscellaneous | 74.6 | 65.7 | 238.4 | 210.4 |
Depreciation, Depletion and Amortization | 306.9 | 269.5 | 852.2 | 765.1 |
Operating Segments |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Consolidated Operating Income (Loss) | 284.7 | 212.5 | 1,298.6 | 1,029.8 |
Regulated Operating Revenue | 1,275.5 | 1,079.6 | 4,746.5 | 3,877.1 |
Cost of energy | 193.7 | 165.9 | 1,103.0 | 755.6 |
Utilities Operating Expense, Maintenance and Operations | 427.9 | 380.6 | 1,291.6 | 1,161.4 |
Taxes, Miscellaneous | 71.1 | 60.8 | 227.1 | 197.3 |
Segment Reporting, Other Segment Item, Amount | 0.1 |  | 1.1 | (0.1) |
Depreciation, Depletion and Amortization | 298.0 | 259.8 | 825.1 | 733.1 |
Operating Segments | Nonrelated Party |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Regulated Operating Revenue | 1,271.9 | 1,076.0 | 4,735.7 | 3,866.7 |
Operating Segments | Related Party |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Regulated Operating Revenue | 3.6 | 3.6 | 10.8 | 10.4 |
Corporate and Other |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Consolidated Operating Income (Loss) | 12.8 | 5.8 |  |  |
Total Assets | 1,300.2 |  | 1,300.2 |  | 1,195.1
Regulated Operating Revenue | 151.8 | 145.9 | 441.8 | 425.1 |
Eliminations |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Regulated Operating Revenue | (154.2) | (149.2) | (449.0) | (434.9) |
Corporate and Other |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Consolidated Operating Income (Loss) |  |  | 21.2 | 8.9 |
Corporate and Other | Unaffiliated |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenues | 1.2 | 0.3 | 3.6 | 0.6 |
Columbia Operations | Unaffiliated |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenues |  |  | 2,326.7 | 1,864.5 |
Columbia Operations | Operating Segments |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Consolidated Operating Income (Loss) | 52.1 | 41.2 | 620.1 | 499.8 |
Total Assets | 15,267.9 |  | 15,267.9 |  | 14,769.5
Regulated Operating Revenue | 488.2 | 426.7 | 2,336.7 | 1,874.1 |
Cost of energy | 58.5 | 34.2 | 548.7 | 319.3 |
Utilities Operating Expense, Maintenance and Operations | 212.8 | 202.9 | 663.5 | 604.9 |
Taxes, Miscellaneous | 52.0 | 45.4 | 171.4 | 149.5 |
Segment Reporting, Other Segment Item, Amount | 0.1 |  | 0.4 | 0.0 |
Depreciation, Depletion and Amortization | 112.7 | 103.0 | 332.6 | 300.6 |
Columbia Operations | Operating Segments | Nonrelated Party |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Regulated Operating Revenue | 484.9 | 423.4 | 2,326.7 | 1,864.5 |
Columbia Operations | Operating Segments | Related Party |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Regulated Operating Revenue | 3.3 | 3.3 | 10.0 | 9.6 |
NIPSCO Operations |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Regulated Operating Revenue | 787.0 | 652.6 |  |  |
NIPSCO Operations | Unaffiliated |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenues |  |  | 2,409.0 | 2,002.2 |
NIPSCO Operations | Intersegment |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenues |  |  |  | 0.8 |
NIPSCO Operations | Operating Segments |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Consolidated Operating Income (Loss) | 232.6 | 171.3 | 678.5 | 530.0 |
Total Assets | 17,834.8 |  | 17,834.8 |  | $ 15,823.5
Regulated Operating Revenue | 787.3 | 652.9 | 2,409.8 | 2,003.0 |
Cost of energy | 135.2 | 131.7 | 554.3 | 436.3 |
Utilities Operating Expense, Maintenance and Operations | 215.1 | 177.7 | 628.1 | 556.5 |
Taxes, Miscellaneous | 19.1 | 15.4 | 55.7 | 47.8 |
Segment Reporting, Other Segment Item, Amount | 0.0 |  | 0.7 | (0.1) |
Depreciation, Depletion and Amortization | 185.3 | 156.8 | 492.5 | $ 432.5 |
NIPSCO Operations | Operating Segments | Nonrelated Party |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Regulated Operating Revenue | 787.0 | 652.6 | 2,409.0 |  |
NIPSCO Operations | Operating Segments | Related Party |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Regulated Operating Revenue | $ 0.3 | $ 0.3 | $ 0.8 |  |

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