Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Property, Plant and Equipment [Line Items]
Total gross property, plant and equipment	$ 10,344.9	$ 9,566.5
Less accumulated depreciation	(2,110.7)	(1,936.6)
Property, plant and equipment	8,234.2	7,629.9
Corporate, Non-Segment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	0.3	0.4
Construction work-in-progress, gross	13.8	10.3
Total gross property, plant and equipment	14.1	10.7
Less accumulated depreciation	0.2	0.0
Property, plant and equipment	$ 14.3	$ 10.7
Production, Gas \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	44 years	43 years
Production, Gas \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		24 years
Production, Gas \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		45 years
Gas transmission \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	57 years	58 years
Gas transmission \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		32 years
Gas transmission \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		73 years
Gas distribution \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	57 years	57 years
Gas distribution \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		48 years
Gas distribution \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		61 years
Gas, Storage \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	42 years	42 years
Gas, Storage \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		36 years
Gas, Storage \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		47 years
General \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	22 years	22 years
General \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		20 years
General \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		25 years
Electric Utilities
Property, Plant and Equipment [Line Items]
Total plant in service before construction work in progress	$ 4,987.4	$ 4,576.2
Construction work-in-progress	270.1	259.4
Property, Plant and Equipment	5,257.5	4,835.6
Less accumulated depreciation	(1,366.5)	(1,280.3)
Property, plant and equipment	$ 3,891.0	3,555.3
Electric Utilities \| Wyodak Plant
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization, remaining amortization period	5 years
Electric Utilities \| Production, Electric
Property, Plant and Equipment [Line Items]
Production, processing and storage	$ 1,545.4	$ 1,508.5
Electric Utilities \| Production, Electric \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	40 years	39 years
Electric Utilities \| Production, Electric \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		32 years
Electric Utilities \| Production, Electric \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		45 years
Electric Utilities \| Electric transmission
Property, Plant and Equipment [Line Items]
Transmission	$ 1,052.3	$ 793.7
Electric Utilities \| Electric transmission \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	48 years	48 years
Electric Utilities \| Electric transmission \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		44 years
Electric Utilities \| Electric transmission \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		51 years
Electric Utilities \| Electric distribution
Property, Plant and Equipment [Line Items]
Distribution	$ 1,347.3	$ 1,238.5
Electric Utilities \| Electric distribution \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	49 years	47 years
Electric Utilities \| Electric distribution \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		45 years
Electric Utilities \| Electric distribution \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		55 years
Electric Utilities \| Integrated Generation
Property, Plant and Equipment [Line Items]
Plant acquisition adjustment	$ 727.3	$ 724.0
Electric Utilities \| Integrated Generation \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	30 years	30 years
Electric Utilities \| Integrated Generation \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		19 years
Electric Utilities \| Integrated Generation \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		38 years
Electric Utilities \| Plant acquisition adjustment
Property, Plant and Equipment [Line Items]
Plant acquisition adjustment	$ 4.9	$ 4.9
Electric Utilities \| Plant acquisition adjustment \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	32 years	32 years
Electric Utilities \| Plant acquisition adjustment \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		32 years
Electric Utilities \| Plant acquisition adjustment \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		32 years
Electric Utilities \| General
Property, Plant and Equipment [Line Items]
General	$ 310.2	$ 306.6
Electric Utilities \| General \| Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	25 years	26 years
Electric Utilities \| General \| Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		16 years
Electric Utilities \| General \| Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		28 years
Gas Utilities
Property, Plant and Equipment [Line Items]
Total plant in service before construction work in progress	$ 5,022.8	$ 4,676.7
Construction work-in-progress, gross	50.5	43.5
Total gross property, plant and equipment	5,073.3	4,720.2
Less accumulated depreciation	(744.4)	(656.3)
Property, plant and equipment	4,328.9	4,063.9
Gas Utilities \| Production, Gas
Property, Plant and Equipment [Line Items]
Production, processing and storage	26.3	21.6
Gas Utilities \| Gas transmission
Property, Plant and Equipment [Line Items]
Transmission	860.0	817.5
Gas Utilities \| Gas distribution
Property, Plant and Equipment [Line Items]
Distribution	3,414.3	3,107.3
Gas Utilities \| Cushion gas - not depreciable
Property, Plant and Equipment [Line Items]
Production, processing and storage	51.4	52.1
Gas Utilities \| Gas, Storage
Property, Plant and Equipment [Line Items]
Production, processing and storage	83.6	78.8
Gas Utilities \| General
Property, Plant and Equipment [Line Items]
General	$ 587.2	$ 599.4

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Property Plant Equipment excluding Construction in Progress

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Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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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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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Amount of acquisition adjustments included in property, plant and equipment (PPE) for utilities.

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Period end amount of construction work in progress in public utility.

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Period end amount of property, plant and equipment (PPE) related to utility distribution.

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Period end amount of property, plant and equipment (PPE) related to generation or processing owned by public utility.

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Period end book value of other property, plant and equipment (PPE) owned (but not classified elsewhere) by the public utility.

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