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Regulatory Matters: Regulatory Matters (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2020
Regulatory assets	$ 480.1	$ 653.0
Regulatory assets, current	(175.7)	(260.3)
Regulatory assets, non-current	304.4	392.7
Regulatory liabilities	566.6	518.6
Regulatory liabilities, current	(98.9)	(46.0)
Regulatory liabilities, non-current	$ 467.7	472.6
Maximum
Gas Price Derivatives - Term of Contract	2 years
Deferred energy and gas costs
Regulatory liabilities	$ 88.9	41.7
Employee benefit plans and related deferred taxes
Regulatory liabilities	36.2	38.9
Cost of removal
Regulatory liabilities	181.9	175.6
Excess deferred income taxes
Regulatory liabilities	247.1	254.8
Other regulatory liabilities
Regulatory liabilities	12.5	7.6
Storm Costs
Regulatory assets	$ 199.6	348.0
Regulatory Asset, Amortization Period	2 years 2 months 12 days
Deferred energy and gas costs
Regulatory assets	$ 55.1	72.6
Deferred gas cost adjustments
Regulatory assets	4.1	12.2
Gas price derivatives
Regulatory assets	5.1	8.8
Deferred taxes on AFUDC
Regulatory assets	7.1	7.3
Employee benefit plans and related deferred taxes
Regulatory assets	89.3	89.3
Environmental
Regulatory assets	2.9	1.3
Loss on reacquired debt
Regulatory assets	17.4	19.2
Deferred taxes on flow through accounting
Regulatory assets	74.7	69.5
Decommissioning costs
Regulatory assets	2.4	3.5
Regulatory Asset, Amortization Period			3 years
Other regulatory assets
Regulatory assets	$ 22.4	$ 21.3

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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.

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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
-Name Accounting Standards Codification
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