Regulatory Matters (Details) $ in Millions	6 Months Ended
Jun. 30, 2025 USD ($)
Schedule of Regulated Operations [Line Items]
Intervenor proposed reduction to base rate revenue request	$ 11.6
Intervenor proposed reduction to PCCAM base	38.4
Requested rate increase (decrease), amount	156.5
Montana Electric Rate Filing
Schedule of Regulated Operations [Line Items]
Regulatory Liability	3.5
Electricity, US Regulated \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	58.0
Public Utilities, Interim Rate Increase (Decrease), Amount	(62.2)
Electricity, US Regulated \| Base electric rate \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	153.8
Public Utilities, Interim Rate Increase (Decrease), Amount	18.4
Electricity, US Regulated \| Base PCCAM rate \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	(94.5)
Public Utilities, Interim Rate Increase (Decrease), Amount	(88.0)
Electricity, US Regulated \| Electric property tax tracker base \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	(1.3)
Public Utilities, Interim Rate Increase (Decrease), Amount	7.4
Electricity, US Regulated \| Settled electric base rate request \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	66.4
Electricity, US Regulated \| Non-settled Base electric rate requested \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	43.9
Electricity, US Regulated \| Base electric rate requested through settlement agreement \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	110.3
Public Utilities, Interim Rate Increase (Decrease), Amount	110.3
Electricity, US Regulated \| Settled electric property tax tracker base \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	(5.2)
Electricity, US Regulated \| Non-settled electric property tax amount \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	4.0
Electricity, US Regulated \| Requested pass through rates for revised interim filing \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	(95.7)
Electricity, US Regulated \| Total revenue requested through revised interim filing \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	14.6
Natural Gas, US Regulated \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	28.0
Public Utilities, Interim Rate Increase (Decrease), Amount	17.6
Natural Gas, US Regulated \| Nebraska
Schedule of Regulated Operations [Line Items]
Public Utilities, Interim Rate Increase (Decrease), Amount	2.3
Public Utilities, Approved Rate Increase (Decrease), Amount	2.4
Natural Gas, US Regulated \| Base gas rate \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	27.9
Public Utilities, Interim Rate Increase (Decrease), Amount	17.4
Natural Gas, US Regulated \| Natural gas property tax tracker base \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	0.1
Public Utilities, Interim Rate Increase (Decrease), Amount	0.2
Natural Gas, US Regulated \| Settled natural gas rate base rate request \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	18.0
Natural Gas, US Regulated \| Base natural gas rate requested through settlement agreement \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	18.0
Natural Gas, US Regulated \| Settled natural gas property tax tracker base \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	0.1
Natural Gas, US Regulated \| Requested pass through rates for revised interim filing \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	0.1
Natural Gas, US Regulated \| Total revenue requested through revised interim filing \| Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 18.1

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Intervenor proposed reduction to PCCAM base

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Amount of public utility's approved rate increase (decrease) by regulatory agency.

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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.

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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

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