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Regulation - Narrative (Details) - Texas - Winter Storm Uri incremental costs - Winter Storm Uri - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended | 31 Months Ended
--- | --- | --- | ---
Mar. 31, 2025 | Sep. 30, 2024 | Mar. 31, 2025
Regulatory Asset [Line Items] |  |  |
Regulatory asset, deferred costs |  |  | $ 32.4
Regulatory asset, recovered cost | $ 3.6 | $ 22.0 |
Regulatory asset, deferred costs, remaining | 6.8 |  | 6.8
Other current assets |  |  |
Regulatory Asset [Line Items] |  |  |
Regulatory asset, deferred costs, remaining | 0.4 |  | 0.4
Deferred charges and other assets |  |  |
Regulatory Asset [Line Items] |  |  |
Regulatory asset, deferred costs, remaining | $ 6.4 |  | $ 6.4

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