Risk Management and Derivatives: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Derivative [Line Items] | |||
| Regulatory assets | $ 394.7 | $ 427.7 | |
| Gas price derivatives | |||
| Derivative [Line Items] | |||
| Regulatory assets | 4.6 | 2.9 | |
| Not Designated as Hedging Instrument | |||
| Derivative [Line Items] | |||
| Derivative, Gain (Loss) on Derivative, Net | $ (0.3) | $ 0.7 | $ (4.2) |
| 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 |
| Not Designated as Hedging Instrument | Natural Gas | |||
| Derivative [Line Items] | |||
| Derivative, Gain (Loss) on Derivative, Net | $ (0.3) | $ 0.7 | $ (4.2) |
| 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 |