Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Revenue from Contract with Customer, Excluding Assessed Tax	$ 259.6	$ 187.5	$ 645.6	$ 507.0
RTO Revenue	16.2	12.5	46.3	39.5
RTO Capacity Revenue	0.5	1.8	3.8	4.0
Revenues	262.1	188.2	652.3	511.5
Contract with Customer, Asset, before Allowance for Credit Loss	81.0		81.0		$ 61.5
Subsidiaries [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	257.4	185.3	638.9	500.3
RTO Revenue	16.2	12.5	46.2	39.4
RTO Capacity Revenue	0.5	1.8	3.8	4.0
Revenues	259.9	186.1	645.6	504.8
Contract with Customer, Asset, before Allowance for Credit Loss	80.0		80.0		$ 60.8
Utility [Member]
RTO Revenue	16.2	12.5	46.2	39.4
RTO Capacity Revenue	0.5	1.8	3.8	4.0
Revenues	259.9	186.1	645.6	504.8
Corporate and Other
RTO Revenue	0.0	0.0	0.1	0.1
RTO Capacity Revenue	0.0	0.0	0.0	0.0
Revenues	3.2	3.1	9.9	9.9
Adjustments and Eliminations
RTO Revenue	0.0	0.0	0.0	0.0
RTO Capacity Revenue	0.0	0.0	0.0	0.0
Revenues	(1.0)	(1.0)	(3.2)	(3.2)
Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	2.4	2.4	7.2	7.2
Other non-606 revenue	2.5	0.7	6.7	4.5
Other Revenues [Member] | Subsidiaries [Member]
Other non-606 revenue	2.5	0.8	6.7	4.5
Other Revenues [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Other non-606 revenue	2.5	0.8	6.7	4.5
Other Revenues [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	2.4	2.4	7.2	7.2
Other non-606 revenue	0.8	0.7	2.6	2.6
Other Revenues [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Other non-606 revenue	(0.8)	(0.8)	(2.6)	(2.6)
Wholesale Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	13.2	6.6	31.5	14.8
Wholesale Revenue [Member] | Subsidiaries [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	13.4	6.8	32.1	15.4
Wholesale Revenue [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	13.4	6.8	32.1	15.4
Wholesale Revenue [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Wholesale Revenue [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	(0.2)	(0.2)	(0.6)	(0.6)
Retail Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	227.3	164.2	556.8	441.5
Retail Revenue [Member] | Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	147.0	103.3	350.6	279.3
Retail Revenue [Member] | Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	50.5	35.0	123.5	90.5
Retail Revenue [Member] | Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	20.6	16.0	55.4	42.4
Retail Revenue [Member] | Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	6.2	7.0	18.2	19.9
Retail Revenue [Member] | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	3.0	2.9	9.1	9.4
Retail Revenue [Member] | Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	227.3	164.2	556.8	441.5
Retail Revenue [Member] | Utility [Member] | Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	147.0	103.3	350.6	279.3
Retail Revenue [Member] | Utility [Member] | Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	50.5	35.0	123.5	90.5
Retail Revenue [Member] | Utility [Member] | Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	20.6	16.0	55.4	42.4
Retail Revenue [Member] | Utility [Member] | Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	6.2	7.0	18.2	19.9
Retail Revenue [Member] | Utility [Member] | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	3.0	2.9	9.1	9.4
Retail Revenue [Member] | Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Retail Revenue [Member] | Corporate and Other | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	0.0	0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations
Revenue from Contract with Customer, Excluding Assessed Tax	0.0		0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0.0	$ 0.0	0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0.0		0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0.0		0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	0.0		0.0	0.0
Retail Revenue [Member] | Adjustments and Eliminations | Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 0.0		$ 0.0	$ 0.0