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Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total gross property, plant and equipment	$ 8,917.2	$ 8,374.8
Less accumulated depreciation and depletion	(1,797.9)	(1,576.8)
Property, plant and equipment	7,119.3	6,798.0
Corporate, Non-Segment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	5.7	5.7
Construction in progress, gross	13.6	13.7
Total gross property, plant and equipment	19.3	19.4
Less accumulated depreciation and depletion	(1.9)	(1.8)
Property, plant and equipment	$ 17.4	$ 17.6
Weighted Average | Corporate, Non-Segment
Property, Plant and Equipment [Line Items]
Weighted average useful life	10 years	11 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		23 years
Production, Gas | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	45 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		47 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		72 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	41 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		49 years
General | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	22 years	23 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	$ 4,393.7	$ 4,190.7
Construction work in progress	123.1	153.0
Property, Plant and Equipment	4,516.8	4,343.7
Less accumulated depreciation and depletion	(1,207.7)	(1,104.1)
Property, plant and equipment	$ 3,309.1	3,239.6
Electric Utilities | Wyodak Plant
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization, remaining amortization period	7 years
Electric Utilities | Production, Electric
Property, Plant and Equipment [Line Items]
Production, processing and storage	$ 1,492.8	$ 1,482.1
Electric Utilities | Production, Electric | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	40 years	41 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	$ 737.4	$ 632.9
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	$ 1,146.9	$ 1,082.5
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	$ 720.0	$ 713.5
Electric Utilities | Integrated Generation | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	30 years	31 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	$ 291.7	$ 274.8
Electric Utilities | General | Weighted Average
Property, Plant and Equipment [Line Items]
Weighted average useful life	27 years	27 years
Electric Utilities | General | Minimum
Property, Plant and Equipment [Line Items]
Weighted average useful life		24 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	$ 4,341.9	$ 3,959.7
Construction in progress, gross	39.2	52.0
Total gross property, plant and equipment	4,381.1	4,011.7
Less accumulated depreciation and depletion	(588.3)	(471.0)
Property, plant and equipment	3,792.8	3,540.7
Gas Utilities | Production, Gas
Property, Plant and Equipment [Line Items]
Production, processing and storage	21.0	17.8
Gas Utilities | Gas transmission
Property, Plant and Equipment [Line Items]
Transmission	759.5	695.4
Gas Utilities | Gas distribution
Property, Plant and Equipment [Line Items]
Distribution	2,860.0	2,620.2
Gas Utilities | Cushion gas - not depreciable
Property, Plant and Equipment [Line Items]
Production, processing and storage	58.2	63.1
Gas Utilities | Gas, Storage
Property, Plant and Equipment [Line Items]
Production, processing and storage	71.4	65.8
Gas Utilities | General
Property, Plant and Equipment [Line Items]
General	$ 571.8	$ 497.4

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