Regulated Operations [Line Items]

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- Definition

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

+ References

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

+ Details

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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 Matters (Regulatory Liabilities) (Details) - USD ($)	Dec. 31, 2025	Sep. 30, 2025	Dec. 31, 2024
Regulated Operations [Line Items]
Regulatory Liabilities	$ 1,773,400,000	$ 23.3	$ 1,581,700,000
Regulatory Liability, Current	260,100,000		150,500,000
Regulatory Liability, Noncurrent	1,513,300,000		1,431,200,000
Deferred Derivative Gain (Loss)
Regulated Operations [Line Items]
Regulatory Liabilities	19,200,000		28,700,000
Customer Assistance Programs
Regulated Operations [Line Items]
Regulatory Liabilities	10,600,000		9,400,000
Rate Refunds
Regulated Operations [Line Items]
Regulatory Liabilities	68,900,000		16,600,000
Off-Systems sales sharing
Regulated Operations [Line Items]
Regulatory Liabilities	21,800,000		21,400,000
HLBV Adjustments under ASC 980
Regulated Operations [Line Items]
Regulatory Liabilities	139,400,000		77,000,000.0
Overrecovered Gas And Fuel Costs
Regulated Operations [Line Items]
Regulatory Liabilities	50,600,000		21,400,000
Cost Of Removal
Regulated Operations [Line Items]
Regulatory Liabilities	454,500,000		482,800,000
Regulatory Effects Of Accounting For Income Taxes
Regulated Operations [Line Items]
Regulatory Liabilities	869,300,000		827,000,000.0
Other Postretirement Costs
Regulated Operations [Line Items]
Regulatory Liabilities	28,000,000.0		40,400,000
Other Liabilities
Regulated Operations [Line Items]
Regulatory Liabilities	$ 111,100,000		$ 57,000,000.0