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Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Total gross property, plant and equipment	$ 9,566.5	$ 8,917.2
Less accumulated depreciation	(1,936.6)	(1,797.9)
Property, plant and equipment	7,629.9	7,119.3
Corporate, Non-Segment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	0.4	5.7
Construction work-in-progress, gross	10.3	13.6
Total gross property, plant and equipment	10.7	19.3
Less accumulated depreciation	0.0	(1.9)
Property, plant and equipment	$ 10.7	$ 17.4
Weighted Average | Corporate, Non-Segment
Property, Plant and Equipment [Line Items]
Weighted average useful life	10 years	10 years
Minimum | Corporate, Non-Segment
Property, Plant and Equipment [Line Items]
Weighted average useful life		4 years
Maximum | Corporate, Non-Segment
Property, Plant and Equipment [Line Items]
Weighted average useful life		21 years
Production, Gas | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	43 years	45 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	58 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		48 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		24 years
Electric Utilities
Property, Plant and Equipment [Line Items]
Total plant in service before construction work in progress	$ 4,576.2	$ 4,393.7
Construction work-in-progress	259.4	123.1
Property, Plant and Equipment	4,835.6	4,516.8
Less accumulated depreciation	(1,280.3)	(1,207.7)
Property, plant and equipment	$ 3,555.3	3,309.1
Electric Utilities | Wyodak Plant
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization, remaining amortization period	6 years
Electric Utilities | Production, Electric
Property, Plant and Equipment [Line Items]
Production, processing and storage	$ 1,508.5	$ 1,492.8
Electric Utilities | Production, Electric | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	39 years	40 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		44 years
Electric Utilities | Electric transmission
Property, Plant and Equipment [Line Items]
Transmission	$ 793.7	$ 737.4
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		42 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	$ 1,238.5	$ 1,146.9
Electric Utilities | Electric distribution | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	47 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		50 years
Electric Utilities | Integrated Generation
Property, Plant and Equipment [Line Items]
Plant acquisition adjustment	$ 724.0	$ 720.0
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	$ 306.6	$ 291.7
Electric Utilities | General | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	26 years	27 years
Electric Utilities | General | Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		23 years
Electric Utilities | General | Maximum
Property, Plant and Equipment [Line Items]
Weighted average useful life		27 years
Gas Utilities
Property, Plant and Equipment [Line Items]
Total plant in service before construction work in progress	$ 4,676.7	$ 4,341.9
Construction work-in-progress, gross	43.5	39.2
Total gross property, plant and equipment	4,720.2	4,381.1
Less accumulated depreciation	(656.3)	(588.3)
Property, plant and equipment	4,063.9	3,792.8
Gas Utilities | Production, Gas
Property, Plant and Equipment [Line Items]
Production, processing and storage	21.6	21.0
Gas Utilities | Gas transmission
Property, Plant and Equipment [Line Items]
Transmission	817.5	759.5
Gas Utilities | Gas distribution
Property, Plant and Equipment [Line Items]
Distribution	3,107.3	2,860.0
Gas Utilities | Cushion gas - not depreciable
Property, Plant and Equipment [Line Items]
Production, processing and storage	52.1	58.2
Gas Utilities | Gas, Storage
Property, Plant and Equipment [Line Items]
Production, processing and storage	78.8	71.4
Gas Utilities | General
Property, Plant and Equipment [Line Items]
General	$ 599.4	$ 571.8

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