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Other Commitments And Contingencies (Narrative) (Details)
 3 Months Ended 6 Months Ended 12 Months Ended
Feb. 03, 2025
USD ($)
Jan. 15, 2025
USD ($)
Sep. 18, 2024
USD ($)
May 24, 2024
USD ($)
Mar. 18, 2024
USD ($)
Jun. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
Rate
MW
Dec. 31, 2024
USD ($)
Rate
MW
Jan. 31, 2024
Dec. 31, 2023
USD ($)
Rate
Jun. 17, 2023
Rate
Other Commitments And Contingencies [Line Items]                      
Wind power purchase agreement capacity | MW             600 600      
Major Rail Operators             3 3      
Line of Credit Facility, Amount Outstanding             $ 0 $ 0   $ 0  
Guarantor Obligations, Current Carrying Value             $ 1,127,500,000 $ 1,127,500,000   646,100,000  
Wind Power Purchase Agreement, Purchase Percentage | Rate             100.00% 100.00%      
Accrual for Environmental Loss Contingencies, Gross             $ 91,800,000 $ 91,800,000   80,000,000  
Other Commitment                   $ 250,000,000  
Asset Retirement Obligation, Period Increase (Decrease)             149,700,000        
Payments to Acquire Assets, Investing Activities     $ 153,300,000 $ 114,900,000 $ 110,600,000            
Contractual Obligation             $ 61,700,000 $ 61,700,000      
NIPSCO Holdings II                      
Other Commitments And Contingencies [Line Items]                      
Subsidiary, Ownership Percentage, Noncontrolling Owner                 4.50%    
Subsidiary, Ownership Percentage, Parent | Rate                     19.90%
NIPSCO Holdings II | Director                      
Other Commitments And Contingencies [Line Items]                      
Subsidiary, Ownership Percentage, Parent | Rate                   17.50%  
Subsequent Event                      
Other Commitments And Contingencies [Line Items]                      
Payments to Acquire Assets, Investing Activities $ 217,600,000 $ 336,600,000                  
MGP Sites                      
Other Commitments And Contingencies [Line Items]                      
Number of waste disposal sites identified by program             51 51      
Liability for estimated remediation costs             $ 86,400,000 $ 86,400,000   $ 73,700,000  
Reasonably possible remediation costs variance from reserve             16,300,000 16,300,000      
Increase (Decrease) in Other Accrued Liabilities           $ 11,200,000          
Asset Retirement Obligation, Period Increase (Decrease)               $ 149,700,000      
Coal Transportation | Maximum                      
Other Commitments And Contingencies [Line Items]                      
Long Term Purchase Commitment Expiration Year               2025      
Pipeline Service Agreements [Member] | Maximum                      
Other Commitments And Contingencies [Line Items]                      
Long Term Purchase Commitment Expiration Year               2038      
Pipeline Service Agreements [Member] | Minimum                      
Other Commitments And Contingencies [Line Items]                      
Long Term Purchase Commitment Expiration Year               2028      
IT Service Agreements [Member] | Maximum                      
Other Commitments And Contingencies [Line Items]                      
Long Term Purchase Commitment Expiration Year               2029      
Standby Letters of Credit                      
Other Commitments And Contingencies [Line Items]                      
Line of Credit Facility, Amount Outstanding             $ 9,400,000 $ 9,400,000   $ 9,900,000