Financing: Debt Covenants (Additional Information) (Details) $ in Millions	Jun. 30, 2026 USD ($)	Dec. 31, 2025 USD ($)
Line of Credit Facility [Line Items]
Consolidated indebtedness to capitalization ratio	0.53
Refundable advances for construction	$ 285.0	$ 0.0
Maximum
Line of Credit Facility [Line Items]
Consolidated indebtedness to capitalization ratio	0.65
Wyoming Electric
Line of Credit Facility [Line Items]
Consolidated indebtedness to capitalization ratio	0.48
Refundable advances for construction	$ 285.0
Wyoming Electric \| Maximum
Line of Credit Facility [Line Items]
Consolidated indebtedness to capitalization ratio	0.6

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details