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Risk Management and Derivatives: Derivatives Not Designated as Hedge Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Derivative [Line Items]
Regulatory assets	$ 391.2		$ 391.2		$ 427.7
Regulatory liabilities	576.6		576.6		568.7
Gas price derivatives
Derivative [Line Items]
Regulatory assets	4.9		4.9		$ 2.9
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ (0.6)	$ (0.3)	$ 0.0	$ 0.4
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold
Not Designated as Hedging Instrument | Natural Gas
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ (0.6)	$ (0.3)	$ 0.0	$ 0.4
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold	Fuel, Purchased Power and Cost of Gas Sold

X

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

Reference 2: http://www.xbrl.org/2003/role/exampleRef
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-Section 55
-Paragraph 10
-SubTopic 10
-Topic 825
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482881/825-10-55-10

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Indicates line item in statement of income or comprehensive income that includes gain (loss) from derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
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-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
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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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 6A
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 5
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-Publisher FASB
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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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
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