Revenue from Contracts with Customers Disaggregation of Revenue (Tables)

9 Months Ended

Sep. 30, 2022

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue [Table Text Block]

The following tables disaggregate our revenue by major source and customer class (in millions):

	Three Months Ended
	September 30, 2022						September 30, 2021
	Electric		Natural Gas		Total		Electric		Natural Gas		Total
Montana	$	85.2	$	10.8	$	96.0	$	85.5	$	9.9	$	95.4
South Dakota	19.0		2.4		21.4		18.8		2.2		21.0
Nebraska	—		3.2		3.2		—		2.5		2.5
Residential	104.2		16.4		120.6		104.3		14.6		118.9
Montana	92.6		7.1		99.7		95.2		6.1		101.3
South Dakota	29.1		2.1		31.2		28.8		1.8		30.6
Nebraska	—		2.3		2.3		—		1.5		1.5
Commercial	121.7		11.5		133.2		124.0		9.4		133.4
Industrial	9.7		0.1		9.8		9.2		—		9.2
Lighting, governmental, irrigation, and interdepartmental	12.6		0.2		12.8		13.1		0.1		13.2
Total Customer Revenues	248.2		28.2		276.4		250.6		24.1		274.7
Other tariff and contract based revenues	22.3		8.6		30.9		26.9		8.7		35.6
Total Revenue from Contracts with Customers	270.5		36.8		307.3		277.5		32.8		310.3
Regulatory amortization and other	21.8		6.0		27.8		10.0		5.7		15.7
Total Revenues	$	292.3	$	42.8	$	335.1	$	287.5	$	38.5	$	326.0

	Nine Months Ended
	September 30, 2022						September 30, 2021
	Electric		Natural Gas		Total		Electric		Natural Gas		Total
Montana	$	252.9	$	91.7	$	344.6	$	251.4	$	82.4	$	333.8
South Dakota	55.0		31.7		86.7		51.0		18.7		69.7
Nebraska	—		26.0		26.0		—		14.6		14.6
Residential	307.9		149.4		457.3		302.4		115.7		418.1
Montana	263.4		48.9		312.3		266.6		42.9		309.5
South Dakota	83.2		23.0		106.2		77.0		12.6		89.6
Nebraska	—		16.0		16.0		—		7.7		7.7
Commercial	346.6		87.9		434.5		343.6		63.2		406.8
Industrial	28.4		0.9		29.3		28.1		0.7		28.8
Lighting, governmental, irrigation, and interdepartmental	25.4		1.4		26.8		26.8		1.0		27.8
Total Customer Revenues	708.3		239.6		947.9		700.9		180.6		881.5
Other tariff and contract based revenues	64.0		27.8		91.8		69.2		27.5		96.7
Total Revenue from Contracts with Customers	772.3		267.4		1,039.7		770.1		208.1		978.2
Regulatory amortization and other	35.1		(22.2)		12.9		28.9		17.9		46.8
Total Revenues	$	807.4	$	245.2	$	1,052.6	$	799.0	$	226.0	$	1,025.0