v3.25.2
Business Segment Information (Schedule Of Operating Income Derived From Revenues And Expenses By Segment) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Dec. 31, 2024
Segment Reporting Information [Line Items]          
Consolidated Operating Income (Loss) $ 262.9 $ 237.0 $ 1,022.3 $ 820.4  
Total Assets 34,028.9   34,028.9   $ 31,788.1
Regulated Operating Revenue 1,283.0 1,084.7 3,466.2 2,791.0  
Cost of energy 261.8 164.7 909.3 589.7  
Utilities Operating Expense, Maintenance and Operations 396.2 357.7 824.0 736.1  
Taxes, Miscellaneous 74.2 67.3 163.8 144.7  
Depreciation, Depletion and Amortization 286.7 253.5 545.3 495.6  
Operating Segments          
Segment Reporting Information [Line Items]          
Consolidated Operating Income (Loss) 256.2 238.9 1,013.9 817.3  
Regulated Operating Revenue 1,285.5 1,087.9 3,471.0 2,797.5  
Cost of energy 261.8 164.7 909.3 589.7  
Utilities Operating Expense, Maintenance and Operations 418.7 378.8 863.7 780.8  
Taxes, Miscellaneous 70.5 63.2 156.0 136.5  
Segment Reporting, Other Segment Item, Amount 0.7 (0.1) 1.0 (0.1)  
Depreciation, Depletion and Amortization 277.6 242.4 527.1 473.3  
Operating Segments | Nonrelated Party          
Segment Reporting Information [Line Items]          
Regulated Operating Revenue 1,281.8 1,084.6 3,463.8 2,790.7  
Operating Segments | Related Party          
Segment Reporting Information [Line Items]          
Regulated Operating Revenue 3.7 3.3 7.2 6.8  
Corporate and Other          
Segment Reporting Information [Line Items]          
Consolidated Operating Income (Loss) 6.7 (1.9)      
Total Assets 1,534.9   1,534.9   1,195.1
Regulated Operating Revenue 144.6 139.1 290.0 279.2  
Eliminations          
Segment Reporting Information [Line Items]          
Regulated Operating Revenue (147.1) (142.3) (294.8) (285.7)  
Corporate and Other          
Segment Reporting Information [Line Items]          
Consolidated Operating Income (Loss)     8.4 3.1  
Corporate and Other | Unaffiliated          
Segment Reporting Information [Line Items]          
Revenues 1.2 0.1 2.4 0.3  
Columbia Operations | Unaffiliated          
Segment Reporting Information [Line Items]          
Revenues     1,841.8 1,441.1  
Columbia Operations | Operating Segments          
Segment Reporting Information [Line Items]          
Consolidated Operating Income (Loss) 122.2 96.6 568.0 458.6  
Total Assets 14,982.7   14,982.7   14,769.5
Regulated Operating Revenue 604.7 490.5 1,848.5 1,447.4  
Cost of energy 110.4 56.3 490.2 285.1  
Utilities Operating Expense, Maintenance and Operations 207.7 191.3 450.7 402.0  
Taxes, Miscellaneous 52.4 46.9 119.4 104.1  
Segment Reporting, Other Segment Item, Amount 0.3 0.0 0.3 0.0  
Depreciation, Depletion and Amortization 111.7 99.4 219.9 197.6  
Columbia Operations | Operating Segments | Nonrelated Party          
Segment Reporting Information [Line Items]          
Regulated Operating Revenue 601.2 487.4 1,841.8 1,441.1  
Columbia Operations | Operating Segments | Related Party          
Segment Reporting Information [Line Items]          
Regulated Operating Revenue 3.5 3.1 6.7 6.3  
NIPSCO Operations          
Segment Reporting Information [Line Items]          
Regulated Operating Revenue 680.6 597.2      
NIPSCO Operations | Unaffiliated          
Segment Reporting Information [Line Items]          
Revenues     1,622.0 1,349.6  
NIPSCO Operations | Intersegment          
Segment Reporting Information [Line Items]          
Revenues       0.5  
NIPSCO Operations | Operating Segments          
Segment Reporting Information [Line Items]          
Consolidated Operating Income (Loss) 134.0 142.3 445.9 358.7  
Total Assets 17,511.3   17,511.3   $ 15,823.5
Regulated Operating Revenue 680.8 597.4 1,622.5 1,350.1  
Cost of energy 151.4 108.4 419.1 304.6  
Utilities Operating Expense, Maintenance and Operations 211.0 187.5 413.0 378.8  
Taxes, Miscellaneous 18.1 16.3 36.6 32.4  
Segment Reporting, Other Segment Item, Amount 0.4 (0.1) 0.7 (0.1)  
Depreciation, Depletion and Amortization 165.9 143.0 307.2 $ 275.7  
NIPSCO Operations | Operating Segments | Nonrelated Party          
Segment Reporting Information [Line Items]          
Regulated Operating Revenue 680.6 597.2 1,622.0    
NIPSCO Operations | Operating Segments | Related Party          
Segment Reporting Information [Line Items]          
Regulated Operating Revenue $ 0.2 $ 0.2 $ 0.5