v3.25.4
Other Commitments And Contingencies (Narrative) (Details)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Dec. 31, 2025
USD ($)
Rate
MW
Oct. 31, 2025
USD ($)
Oct. 30, 2025
USD ($)
Oct. 28, 2025
USD ($)
Rate
Sep. 04, 2025
USD ($)
Jun. 18, 2025
USD ($)
May 31, 2025
USD ($)
Feb. 03, 2025
USD ($)
Jan. 15, 2025
USD ($)
Sep. 30, 2025
USD ($)
Dec. 31, 2024
USD ($)
Dec. 31, 2025
USD ($)
Rate
MW
Dec. 31, 2024
USD ($)
Jan. 31, 2024
Jun. 17, 2023
Rate
Other Commitments And Contingencies [Line Items]                              
Wind power purchase agreement capacity | MW 1,200                     1,200      
Major Rail Operators 3                     3      
Line of Credit Facility, Amount Outstanding $ 0.0                   $ 0.0 $ 0.0 $ 0.0    
Guarantor Obligations, Current Carrying Value $ 27.2                   1,127.5 $ 27.2 1,127.5    
Wind Power Purchase Agreement, Purchase Percentage | Rate 100.00%                     100.00%      
Accrual for Environmental Loss Contingencies, Gross $ 82.6                   91.8 $ 82.6 91.8    
Asset Retirement Obligation, Period Increase (Decrease)                     48.9        
Payments to Acquire Assets, Investing Activities 3.6   $ 4.2     $ 262.4 $ 141.4 $ 217.6 $ 336.6            
Contractual Obligation $ 52.0                     52.0      
Proceeds from Contributed Capital   $ 175.0                   $ 344.9 2,160.0    
Business Combination, Price of Acquisition, Expected       $ 35.2                      
NIPSCO Holdings II                              
Other Commitments And Contingencies [Line Items]                              
Subsidiary, Ownership Percentage, Noncontrolling Owner       14.90%                   4.50%  
Subsidiary, Ownership Percentage, Parent | Rate       19.90%                     19.90%
Blackstone Investor                              
Other Commitments And Contingencies [Line Items]                              
Subsidiary, Ownership Percentage, Parent | Rate       19.90%                      
MGP Sites                              
Other Commitments And Contingencies [Line Items]                              
Number of waste disposal sites identified by program 41                     41      
Liability for estimated remediation costs $ 75.5                   86.4 $ 75.5 86.4    
Reasonably possible remediation costs variance from reserve 16.5                     $ 16.5      
CCR Remediation                              
Other Commitments And Contingencies [Line Items]                              
Accrual for Environmental Loss Contingencies, Period Increase (Decrease)                   $ 48.9          
Pipeline Service Agreements [Member] | Maximum                              
Other Commitments And Contingencies [Line Items]                              
Long Term Purchase Commitment Expiration Year                       2044      
Pipeline Service Agreements [Member] | Minimum                              
Other Commitments And Contingencies [Line Items]                              
Long Term Purchase Commitment Expiration Year                       2030      
IT Service Agreements [Member] | Maximum                              
Other Commitments And Contingencies [Line Items]                              
Long Term Purchase Commitment Expiration Year                       2030      
Standby Letters of Credit                              
Other Commitments And Contingencies [Line Items]                              
Line of Credit Facility, Amount Outstanding $ 119.0                   $ 9.4 $ 119.0 $ 9.4    
Payments to Acquire Assets, Investing Activities         $ 133.7