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Summary of Significant Accounting Policies - Components of Accrued Revenue (Detail) - USD ($) $ in Millions		Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Deferred Revenue Arrangement [Line Items]
Regulatory Asset, Current	[1]	$ 61.3	$ 56.5	$ 53.5
Total Accrued Revenue		65.4	63.4	57.3
Regulatory Assets
Deferred Revenue Arrangement [Line Items]
Regulatory Asset, Current		61.3	56.5	53.5
Unbilled Revenues
Deferred Revenue Arrangement [Line Items]
Regulatory Asset, Current		$ 4.1	$ 6.9	$ 3.8
[1] Reflects amounts included in the Accrued Revenue on the Company’s Consolidated Balance Sheets.

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No definition available.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 340
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478742/980-340-50-1

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Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 912
-SubTopic 310
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478345/912-310-45-2

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