Revenue from Contracts with Customers Disaggregation of Revenue (Tables)

12 Months Ended

Dec. 31, 2024

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue [Table Text Block]

The following tables disaggregate our revenue for the twelve months ended by major source and customer class (in millions):

December 31, 2024	Electric		Natural Gas		Total
Montana	398.8		110.2		509.0
South Dakota	70.0		26.9		96.9
Nebraska	—		21.2		21.2
Residential	468.8		158.3		627.1
Montana	409.0		59.9		468.9
South Dakota	111.8		18.1		129.9
Nebraska	—		11.4		11.4
Commercial	520.8		89.4		610.2
Industrial	46.6		1.0		47.6
Lighting, governmental, irrigation, and interdepartmental	32.8		1.4		34.2
Total Retail Revenues	1,069.0		250.1		1,319.1
Regulatory Amortization	24.9		19.0		43.9
Transmission	97.1		—		97.1
Wholesale and other	9.7		44.1		53.8
Total Revenues	$	1,200.7	$	313.2	$	1,513.9

December 31, 2023	Electric		Natural Gas		Total
Montana	408.3		136.1		544.4
South Dakota	67.9		36.6		104.5
Nebraska	—		35.5		35.5
Residential	476.2		208.2		684.4
Montana	431.4		73.7		505.1
South Dakota	103.2		25.9		129.1
Nebraska	—		22.1		22.1
Commercial	534.6		121.7		656.3
Industrial	46.0		1.4		47.4
Lighting, governmental, irrigation, and interdepartmental	32.7		1.7		34.4
Total Retail Revenues	1,089.5		333.0		1,422.5
Regulatory Amortization	(105.6)		(25.0)		(130.6)
Transmission	78.4		—		78.4
Wholesale and other	6.5		45.3		51.8
Total Revenues(1)	$	1,068.8	$	353.3	$	1,422.1

December 31, 2022	Electric		Natural Gas		Total
Montana	357.4		152.3		509.7
South Dakota	69.8		39.2		109.0
Nebraska	—		35.8		35.8
Residential	427.2		227.3		654.5
Montana	368.6		79.3		447.9
South Dakota	108.2		28.5		136.7
Nebraska	—		22.1		22.1
Commercial	476.8		129.9		606.7
Industrial	39.8		1.5		41.3
Lighting, governmental, irrigation, and interdepartmental	31.0		1.9		32.9
Total Retail Revenues	974.8		360.6		1,335.4
Regulatory Amortization	46.4		(28.1)		18.3
Transmission	77.8		—		77.8
Wholesale and other	7.6		38.7		46.3
Total Revenues(1)	$	1,106.6	$	371.2	$	1,477.8