v3.26.1
Other Commitments And Contingencies (Narrative) (Details)
$ in Millions
3 Months Ended 6 Months Ended
Oct. 28, 2025
USD ($)
Rate
Jun. 30, 2026
USD ($)
Rate
MW
Jun. 30, 2026
USD ($)
Rate
MW
Dec. 31, 2025
USD ($)
Other Commitments And Contingencies [Line Items]        
Guaranty Liabilities   $ 27.2 $ 27.2  
Recorded reserves to cover environmental remediation at various sites   $ 80.2 $ 80.2 $ 82.6
Wind Power Purchase Agreement, Purchase Percentage | Rate   100.00% 100.00%  
Business Combination, Price of Acquisition, Expected $ 35.2      
Contractual Obligation   $ 52.2 $ 52.2 52.0
Long-Term Purchase Commitment, Amount   658.7    
Noncancelable Commitments - e-storage   122.7 122.7  
Guarantor Obligations, Maximum Exposure, Undiscounted   $ 245.4 245.4  
2028 through 2030 market capacity purchase commitments     174.6  
Capacity Purchase Commitments     $ 1,100.0  
NIPSCO Holdings II        
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   36 36  
Liability for Estimated Remediation Costs   $ 72.6 $ 72.6 $ 75.5
us-gaap_VariableInterestEntityPrimaryBeneficiaryMemberGenCo        
Other Commitments And Contingencies [Line Items]        
Nameplate Capacity | MW   167 167  
Standby Letters of Credit        
Other Commitments And Contingencies [Line Items]        
Long-term Line of Credit   $ 119.0 $ 119.0