XML 59 R51.htm IDEA: XBRL DOCUMENT v3.24.2.u1
Risk Management and Derivatives: Derivatives Not Designated as Hedge Instruments (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2024
Jun. 30, 2023
Jun. 30, 2024
Jun. 30, 2023
Dec. 31, 2023
Derivative [Line Items]          
Regulatory assets $ 424.8   $ 424.8   $ 480.1
Regulatory liabilities 557.4   557.4   566.6
Gas price derivatives          
Derivative [Line Items]          
Regulatory assets 0.5   0.5   $ 5.1
Not Designated as Hedging Instrument          
Derivative [Line Items]          
Derivative, Gain (Loss) on Derivative, Net $ 0.1 $ 0.4 $ 0.7 $ (2.7)  
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Fuel, Purchased Power and Cost of Gas Sold Fuel, Purchased Power and Cost of Gas Sold Fuel, Purchased Power and Cost of Gas Sold Fuel, Purchased Power and Cost of Gas Sold  
Not Designated as Hedging Instrument | Natural Gas          
Derivative [Line Items]          
Derivative, Gain (Loss) on Derivative, Net $ 0.1 $ 0.4 $ 0.7 $ (2.7)  
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Fuel, Purchased Power and Cost of Gas Sold Fuel, Purchased Power and Cost of Gas Sold Fuel, Purchased Power and Cost of Gas Sold Fuel, Purchased Power and Cost of Gas Sold