Rate Matters (Details) - USD ($) $ in Millions |
6 Months Ended | 12 Months Ended | |||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jun. 30, 2026 |
Dec. 31, 2027 |
Dec. 31, 2025 |
Dec. 31, 2024 |
[2] | |||||||||||||||
| Fuel Rules [Abstract] | |||||||||||||||||||
| Deferred fuel rules monitored costs | $ 6.7 | [1] | $ 7.1 | [2] | $ 3.0 | ||||||||||||||
| Electric Rate Proceeding [Member] | PSCW [Member] | MGE [Member] | |||||||||||||||||||
| Rate Proceedings [Abstract] | |||||||||||||||||||
| Proposed rate increase (decrease), percentage | [3],[4] | 0.15% | |||||||||||||||||
| Proposed return on equity, percentage | 9.80% | ||||||||||||||||||
| Proposed equity capital structure, percentage | 56.10% | ||||||||||||||||||
| Authorized rate increase (decrease), percentage | [3],[5],[6] | 2.63% | |||||||||||||||||
| Authorized return on equity, percentage | 9.70% | ||||||||||||||||||
| Approved equity capital structure, percentage | 56.10% | ||||||||||||||||||
| Fuel Rules [Abstract] | |||||||||||||||||||
| Fuel rules, bandwidth | 2.00% | 2.00% | |||||||||||||||||
| Electric Rate Proceeding [Member] | PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member] | |||||||||||||||||||
| Rate Proceedings [Abstract] | |||||||||||||||||||
| Proposed rate increase (decrease), percentage | [3],[4] | 3.63% | |||||||||||||||||
| Proposed return on equity, percentage | 9.80% | ||||||||||||||||||
| Proposed equity capital structure, percentage | 56.10% | ||||||||||||||||||
| Gas Rate Proceeding [Member] | PSCW [Member] | MGE [Member] | |||||||||||||||||||
| Rate Proceedings [Abstract] | |||||||||||||||||||
| Proposed rate increase (decrease), percentage | [3],[4] | 2.77% | |||||||||||||||||
| Proposed return on equity, percentage | 9.80% | ||||||||||||||||||
| Proposed equity capital structure, percentage | 56.10% | ||||||||||||||||||
| Authorized rate increase (decrease), percentage | [3],[6] | 1.32% | |||||||||||||||||
| Authorized return on equity, percentage | 9.70% | ||||||||||||||||||
| Approved equity capital structure, percentage | 56.10% | ||||||||||||||||||
| Gas Rate Proceeding [Member] | PSCW [Member] | Rate Matters For Future Periods [Member] | MGE [Member] | |||||||||||||||||||
| Rate Proceedings [Abstract] | |||||||||||||||||||
| Proposed rate increase (decrease), percentage | [3],[4] | 2.04% | |||||||||||||||||
| Proposed return on equity, percentage | 9.80% | ||||||||||||||||||
| Proposed equity capital structure, percentage | 56.10% | ||||||||||||||||||
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