v3.26.1
Long-Term Debt (Narrative) (Details)
May 26, 2026
USD ($)
Jun. 30, 2026
USD ($)
MW
May 18, 2026
USD ($)
Standby Letters of Credit      
Debt Instrument [Line Items]      
Revolving credit facility interest rate of 2.13% at March 31, 2020   $ 119,000,000.0  
Rosewater      
Debt Instrument [Line Items]      
Nameplate Capacity | MW   102  
Senior Notes | NiSource      
Debt Instrument [Line Items]      
Senior Notes $ 500,000,000.0   $ 750,000,000.0
Debt, Weighted Average Interest Rate   4.75%  
Proceeds from Debt, Net of Issuance Costs $ 1,236,000,000    
Unsecured Debt | NiSource      
Debt Instrument [Line Items]      
Debt, Weighted Average Interest Rate   5.30%