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Regulatory Matters: Regulatory Matters (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Regulatory assets	$ 427.7	$ 480.1
Regulatory assets, current	(154.8)	(175.7)
Regulatory assets, non-current	272.9	304.4
Regulatory liabilities	568.7	566.6
Regulatory liabilities, current	(94.1)	(98.9)
Regulatory liabilities, non-current	$ 474.6	467.7
Maximum
Gas Price Derivatives - Term of Contract	2 years
Deferred energy and gas costs
Regulatory liabilities	$ 91.9	88.9
Employee benefit plans and related deferred taxes
Regulatory liabilities	36.7	36.2
Cost of removal
Regulatory liabilities	197.0	181.9
Excess deferred income taxes
Regulatory liabilities	238.5	247.1
Other regulatory liabilities
Regulatory liabilities	4.6	12.5
Storm Costs
Regulatory assets	$ 109.5	199.6
Regulatory Asset, Amortization Period	1 year 7 months 6 days
Deferred energy and gas costs
Regulatory assets	$ 62.8	55.1
Deferred gas cost adjustments
Regulatory assets	14.5	4.1
Gas price derivatives
Regulatory assets	2.9	5.1
Deferred taxes on AFUDC
Regulatory assets	8.0	7.1
Employee benefit plans and related deferred taxes
Regulatory assets	89.0	89.3
Environmental
Regulatory assets	10.7	2.9
Loss on reacquired debt
Regulatory assets	15.7	17.4
Deferred taxes on flow through accounting
Regulatory assets	87.7	74.7
Decommissioning costs
Regulatory assets	2.4	2.4
Other regulatory assets
Regulatory assets	$ 24.5	$ 22.4

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
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