The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 405
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477571/980-405-25-1

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

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- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(24))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

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Regulatory Liabilities (Detail) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 73.5	$ 64.0	$ 57.8
Less: Current Portion of Regulatory Liabilities	21.0	17.2	24.5
Regulatory Liabilities – noncurrent	52.5	46.8	33.3
Income Taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	49.7	50.4	37.2	$ 48.9
Rate Adjustment Mechanisms
Regulatory Liabilities [Line Items]
Regulatory Liabilities	17.8	$ 13.6	$ 20.6
Retirement Benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 6.0