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Regulatory Matters: Regulatory Matters (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Regulatory assets	$ 391.2	$ 427.7
Regulatory assets, current	(138.2)	(154.8)
Regulatory assets, non-current	253.0	272.9
Regulatory liabilities	576.6	568.7
Regulatory liabilities, current	(91.9)	(94.1)
Regulatory liabilities, non-current	484.7	474.6
Deferred energy and gas costs
Regulatory liabilities	61.1	67.8
Employee benefit plan costs and related deferred taxes
Regulatory liabilities	35.0	36.7
Cost of removal
Regulatory liabilities	212.0	197.0
Excess deferred income taxes
Regulatory liabilities	232.4	238.5
Colorado renewable energy
Regulatory liabilities	30.7	24.1
Other regulatory liabilities
Regulatory liabilities	5.4	4.6
Storm Costs
Regulatory assets	62.1	109.5
Deferred energy and gas costs
Regulatory assets	76.1	62.8
Deferred gas cost adjustments
Regulatory assets	7.5	14.5
Gas price derivatives
Regulatory assets	4.9	2.9
Deferred taxes on AFUDC
Regulatory assets	9.5	8.0
Employee benefit plans and related deferred taxes
Regulatory assets	85.7	89.0
Environmental
Regulatory assets	11.5	10.7
Loss on reacquired debt
Regulatory assets	14.5	15.7
Deferred taxes on flow through accounting
Regulatory assets	93.1	87.7
Decommissioning costs
Regulatory assets	2.4	2.4
Other regulatory assets
Regulatory assets	$ 23.9	$ 24.5

X

- Definition

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
-Topic 980
-SubTopic 340
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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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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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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

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