v3.26.3
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, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]          
Consolidated Operating Income (Loss) $ 340.3 $ 297.5 $ 1,387.6 $ 1,319.8  
Total Assets 38,866.8   38,866.8   $ 35,858.7
Regulated Operating Revenue 1,349.4 1,273.1 5,054.9 4,739.3  
Cost of energy 207.3 193.6 1,070.1 1,102.9  
Utilities Operating Expense, Maintenance and Operations 428.5 401.1 1,392.6 1,225.1  
Taxes, Miscellaneous 34.5 74.6 215.3 238.4  
Depreciation, Depletion and Amortization 337.8 306.9 988.3 852.2  
Operating Segments          
Segment Reporting [Line Items]          
Consolidated Operating Income (Loss) 342.3 284.7 1,386.8 1,298.6  
Regulated Operating Revenue 1,341.1 1,275.5 5,051.2 4,746.5  
Cost of energy 204.0 193.7 1,065.8 1,103.0  
Utilities Operating Expense, Maintenance and Operations 435.6 427.9 1,431.0 1,291.6  
Taxes, Miscellaneous 28.9 71.1 200.1 227.1  
Segment Reporting, Other Segment Item, Amount 1.1 0.1 1.1 1.1  
Depreciation, Depletion and Amortization 329.2 298.0 966.4 825.1  
Operating Segments | Nonrelated Party          
Segment Reporting [Line Items]          
Regulated Operating Revenue 1,337.4 1,271.9 5,040.0 4,735.7  
Operating Segments | Related Party          
Segment Reporting [Line Items]          
Regulated Operating Revenue 3.7 3.6 11.2 10.8  
Corporate and Other          
Segment Reporting [Line Items]          
Consolidated Operating Income (Loss) (2.0) 12.8 0.8 21.2  
Total Assets 2,479.7   2,479.7   1,828.3
Regulated Operating Revenue 165.1 151.8 475.8 441.8  
Eliminations          
Segment Reporting [Line Items]          
Regulated Operating Revenue (156.8) (154.2) (472.1) (449.0)  
Corporate and Other | Unaffiliated          
Segment Reporting [Line Items]          
Revenues 12.0 1.2 14.9 3.6  
Columbia Operations | Unaffiliated          
Segment Reporting [Line Items]          
Revenues     2,422.4 2,326.7  
Columbia Operations | Intersegment          
Segment Reporting [Line Items]          
Revenues       10.0  
Columbia Operations | Operating Segments          
Segment Reporting [Line Items]          
Consolidated Operating Income (Loss) 119.2 52.1 694.8 620.1  
Total Assets 16,638.3   16,638.3   15,903.7
Regulated Operating Revenue 505.6 488.2 2,432.7 2,336.7  
Cost of energy 46.5 58.5 511.2 548.7  
Utilities Operating Expense, Maintenance and Operations 204.3 212.8 707.9 663.5  
Taxes, Miscellaneous 8.4 52.0 139.3 171.4  
Segment Reporting, Other Segment Item, Amount 0.7 0.1 0.7 0.4  
Depreciation, Depletion and Amortization 126.5 112.7 378.8 332.6  
Columbia Operations | Operating Segments | Nonrelated Party          
Segment Reporting [Line Items]          
Regulated Operating Revenue 502.2 484.9 2,422.4    
Columbia Operations | Operating Segments | Related Party          
Segment Reporting [Line Items]          
Regulated Operating Revenue 3.4 3.3 10.3    
NIPSCO Operations          
Segment Reporting [Line Items]          
Regulated Operating Revenue 835.2 787.0      
NIPSCO Operations | Unaffiliated          
Segment Reporting [Line Items]          
Revenues       2,409.0  
NIPSCO Operations | Intersegment          
Segment Reporting [Line Items]          
Revenues       0.8  
NIPSCO Operations | Operating Segments          
Segment Reporting [Line Items]          
Consolidated Operating Income (Loss) 223.1 232.6 692.0 678.5  
Total Assets 19,748.8   19,748.8   $ 18,126.7
Regulated Operating Revenue 835.5 787.3 2,618.5 2,409.8  
Cost of energy 157.5 135.2 554.6 554.3  
Utilities Operating Expense, Maintenance and Operations 231.3 215.1 723.1 628.1  
Taxes, Miscellaneous 20.5 19.1 60.8 55.7  
Segment Reporting, Other Segment Item, Amount 0.4 0.0 0.4 0.7  
Depreciation, Depletion and Amortization 202.7 185.3 587.6 $ 492.5  
NIPSCO Operations | Operating Segments | Nonrelated Party          
Segment Reporting [Line Items]          
Regulated Operating Revenue 835.2 787.0 2,617.6    
NIPSCO Operations | Operating Segments | Related Party          
Segment Reporting [Line Items]          
Regulated Operating Revenue $ 0.3 $ 0.3 $ 0.9