v3.26.3
Variable Interest Entities (Narrative) (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Oct. 28, 2025
USD ($)
Rate
Sep. 30, 2026
USD ($)
Rate
MW
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
Rate
MW
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Variable Interest Entity [Line Items]            
Wind Power Purchase Agreement, Purchase Percentage | Rate   100.00%   100.00%    
Income Taxes   $ 13.1 $ 20.6 $ 109.1 $ 150.1  
Contributions from NIPSCO and GenCo minority interest holders       194.4 145.3  
Payments to Noncontrolling Interests   12.5 11.1 59.5 55.5  
Business Combination, Price of Acquisition, Expected $ 35.2          
Current assets [1]   2,363.5   2,363.5   $ 2,377.2
Total Assets   38,866.8   38,866.8   35,858.7
Current liabilities [2]   4,769.9   4,769.9   3,457.4
Public Utilities, Property, Plant and Equipment, Net [1]   31,595.4   31,595.4   28,688.2
Variable Interest Entity Primary Beneficiary Member GenCo            
Variable Interest Entity [Line Items]            
Other Assets   173.2   173.2   305.4
us-gaap_VariableInterestEntityPrimaryBeneficiaryMemberGenCo            
Variable Interest Entity [Line Items]            
Contributions from NIPSCO and GenCo minority interest holders   52.8   100.6 0.0  
Payments to Noncontrolling Interests       0.0    
Current assets   185.1   185.1   62.5
Other Assets   184.4   184.4   305.4
Total Assets   1,014.3   1,014.3   407.6
Current liabilities   74.4   74.4   40.8
Total Liabilities   74.4   74.4   40.8
Public Utilities, Property, Plant and Equipment, Net   634.8   634.8   39.7
Regulatory Assets   10.0   10.0   $ 0.0
NIPSCO Holdings II            
Variable Interest Entity [Line Items]            
Contributions from NIPSCO and GenCo minority interest holders   $ 17.1 $ 11.0 $ 93.8 $ 145.3  
NIPSCO Holdings II            
Variable Interest Entity [Line Items]            
Subsidiary, Ownership Percentage, Parent | Rate 19.90%          
Rosewater            
Variable Interest Entity [Line Items]            
Nameplate Capacity | MW   102   102    
Indiana Crossroads Wind            
Variable Interest Entity [Line Items]            
Nameplate Capacity | MW   302   302    
Indiana Crossroads Solar            
Variable Interest Entity [Line Items]            
Nameplate Capacity | MW   200   200    
Dunns Bridge I            
Variable Interest Entity [Line Items]            
Nameplate Capacity | MW   265   265    
[1] Includes $1,857.3 million and $1,312.7 million at September 30, 2026 and December 31, 2025, respectively, of net property, plant and equipment assets and $228.6 million and $90.1 million at September 30, 2026 and December 31, 2025, respectively, of current assets of consolidated VIEs that may be used only to settle obligations of the consolidated VIEs. Refer to Note 4, "Noncontrolling Interests," for additional information.
(2)Includes $173.2 million and $305.4 million at September 30, 2026 and December 31, 2025, respectively, of advanced deposits of project costs and $10.0 million and zero, respectively, of regulatory assets at September 30, 2026 and December 31, 2025, respectively, of consolidated VIEs that may be used only to settle obligations of the consolidated VIEs. Refer to Note 4, "Noncontrolling Interests," for additional information.
[2] Includes $89.8 million and $56.9 million at September 30, 2026 and December 31, 2025, respectively, of current liabilities and $57.6 million and $55.7 million at September 30, 2026 and December 31, 2025, respectively, of other liabilities, and finance leases of $40.0 million and $40.1 million at September 30, 2026 and December 31, 2025, respectively, of consolidated VIEs that creditors do not have recourse to our general credit. Refer to Note 4, "Noncontrolling Interests," for additional information.