Regulatory Matters (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) Rate
Montana | Electric
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 156.5
Public Utilities, Requested Equity Capital Structure, Percentage | Rate	46.81%
Return on equity, percentage | Rate	10.80%
Forecasted rate base	$ 3,450.0
Public Utilities, Interim Rate Increase (Decrease), Amount	18.4
Montana | Electric | Base electric rate
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	69.4
Montana | Electric | Base PCCAM interim rate
Public Utilities, General Disclosures [Line Items]
Public Utilities, Interim Rate Increase (Decrease), Amount	88.0
Montana | Gas Domestic Regulated [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 28.6
Public Utilities, Requested Equity Capital Structure, Percentage | Rate	46.81%
Return on equity, percentage | Rate	10.80%
Forecasted rate base	$ 731.9
Public Utilities, Interim Rate Increase (Decrease), Amount	17.4
South Dakota | Gas Domestic Regulated [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	6.0
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 4.6
Public Utilities, Approved Rate of Return | Rate	6.91%
Requested Rate base	$ 95.6
Approved Rate base	$ 96.2
Requested Rate of Return | Rate	7.75%
Nebraska | Gas Domestic Regulated [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 3.6
Public Utilities, Requested Equity Capital Structure, Percentage | Rate	53.13%
Requested Rate base	$ 47.4
Return on equity, percentage | Rate	10.70%
Public Utilities, Interim Rate Increase (Decrease), Amount	$ 2.3