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Activity in Company's Allowance for Doubtful Accounts (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Balance at Beginning of Period | $ 2.4 | $ 2.6 | $ 3.3
Provision | 4.3 | 6.4 | 6.7
Recoveries | 0.5 | 0.6 | 0.9
Accounts Written Off | 4.8 | 7.2 | 7.6
Regulatory Defferals | 0.0 | 0.0 | (0.7)
Balance at End of Period | 2.4 | 2.4 | 2.6
Electric |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Balance at Beginning of Period | 1.5 | 1.6 | 2.0
Provision | 2.0 | 3.6 | 4.2
Recoveries | 0.2 | 0.2 | 0.3
Accounts Written Off | 2.3 | 3.9 | 4.4
Regulatory Defferals | 0.0 | 0.0 | (0.5)
Balance at End of Period | 1.4 | 1.5 | 1.6
Gas |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Balance at Beginning of Period | 0.9 | 1.0 | 1.3
Provision | 2.3 | 2.8 | 2.5
Recoveries | 0.3 | 0.4 | 0.6
Accounts Written Off | 2.5 | 3.3 | 3.2
Regulatory Defferals | 0.0 | 0.0 | (0.2)
Balance at End of Period | $ 1.0 | $ 0.9 | $ 1.0

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