Revenue from Contracts with Customers Disaggregation of Revenue (Tables)

12 Months Ended

Dec. 31, 2022

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, 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 Customer Revenues	974.8		360.6		1,335.4
Other Tariff and Contract Based Revenues	85.7		38.3		124.0
Total Revenue from Contracts with Customers	1,060.5		398.9		1,459.4
Regulatory amortization	46.1		(27.7)		18.4
Total Revenues	$	1,106.6	$	371.2	$	1,477.8

December 31, 2021	Electric		Natural Gas		Total
Montana	334.6		126.0		460.6
South Dakota	65.4		26.6		92.0
Nebraska	—		21.0		21.0
Residential	400.0		173.6		573.6
Montana	356.7		64.7		421.4
South Dakota	102.5		19.1		121.6
Nebraska	—		11.4		11.4
Commercial	459.2		95.2		554.4
Industrial	37.9		1.1		39.0
Lighting, Governmental, Irrigation, and Interdepartmental	32.1		1.4		33.5
Total Customer Revenues	929.2		271.3		1,200.5
Other Tariff and Contract Based Revenues	89.5		36.8		126.3
Total Revenue from Contracts with Customers	1,018.7		308.1		1,326.8
Regulatory amortization	33.5		12.0		45.5
Total Revenues	$	1,052.2	$	320.1	$	1,372.3

December 31, 2020	Electric		Natural Gas		Total
Montana	320.8		103.5		424.3
South Dakota	66.6		21.5		88.1
Nebraska	—		16.9		16.9
Residential	387.4		141.9		529.3
Montana	338.3		51.3		389.6
South Dakota	101.1		14.3		115.4
Nebraska	—		8.1		8.1
Commercial	439.4		73.7		513.1
Industrial	36.8		0.9		37.7
Lighting, Governmental, Irrigation, and Interdepartmental	31.8		0.9		32.7
Total Customer Revenues	895.4		217.4		1,112.8
Other Tariff and Contract Based Revenues	58.5		35.5		94.0
Total Revenue from Contracts with Customers	953.9		252.9		1,206.8
Regulatory amortization	(13.1)		5.0		(8.1)
Total Revenues	$	940.8	$	257.9	$	1,198.7