Summary of Significant Accounting Policies - Components of Accrued Revenue (Detail) - USD ($) $ in Millions |
Jun. 30, 2026 |
Dec. 31, 2025 |
Jun. 30, 2025 |
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|---|---|---|---|---|---|
| Deferred Revenue Arrangement [Line Items] | |||||
| Regulatory Assets – Current | [1] | $ 64.8 | $ 78.1 | $ 52.6 | |
| Total Accrued Revenue | 69.5 | 87.0 | 56.8 | ||
| Regulatory Assets | |||||
| Deferred Revenue Arrangement [Line Items] | |||||
| Regulatory Assets – Current | 64.8 | 78.1 | 52.6 | ||
| Unbilled Revenues | |||||
| Deferred Revenue Arrangement [Line Items] | |||||
| Regulatory Assets – Current | $ 4.7 | $ 8.9 | $ 4.2 | ||
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