Regulation and Rates - Colstrip Adjustment Rider (Details) - Subsidiaries - Electricity, US Regulated [Member] - Colstrip Adjustment Rider - USD ($) $ in Millions |
Jan. 01, 2026 |
Dec. 19, 2025 |
Jan. 01, 2025 |
|---|---|---|---|
| Regulatory Assets [Line Items] | |||
| Public Utilities, Approved Rate Increase (Decrease), Amount | $ (82.5) | $ (6.9) | $ 4.1 |
| Public Utilities, Approved Rate Increase (Decrease), Percentage | (2.30%) | (0.20%) | 0.10% |