v3.25.2
Revenue Recognition Revenue Recognition (Allowance for Credit Losses) (Details) - USD ($)
 6 Months Ended 12 Months Ended
Jun. 30, 2025
Dec. 31, 2024
Dec. 31, 2023
Accounts Receivable Allowance For Credit Loss [Line Items]      
Accounts Receivable, Allowance for Credit Loss $ 27,300,000 $ 23,700,000 $ 22,900,000
Current period provisions 27,500,000 38,800,000  
Write-offs charged against allowance 28,600,000 55,700,000  
Recoveries of amounts previously written off 4,700,000 17,700,000  
Corporate and Other      
Accounts Receivable Allowance For Credit Loss [Line Items]      
Accounts Receivable, Allowance for Credit Loss 0 0 800,000
Current period provisions 0 0  
Write-offs charged against allowance 0 (800,000)  
Recoveries of amounts previously written off 0 0  
Columbia Operations      
Accounts Receivable Allowance For Credit Loss [Line Items]      
Accounts Receivable, Allowance for Credit Loss 11,400,000 9,800,000 10,200,000
Current period provisions 20,400,000 26,700,000  
Write-offs charged against allowance 23,100,000 43,900,000  
Recoveries of amounts previously written off 4,300,000 16,800,000  
NIPSCO Operations      
Accounts Receivable Allowance For Credit Loss [Line Items]      
Accounts Receivable, Allowance for Credit Loss 15,900,000 13,900,000 $ 11,900,000
Current period provisions 7,100,000 12,100,000  
Write-offs charged against allowance 5,500,000 11,000,000.0  
Recoveries of amounts previously written off $ 400,000 $ 900,000