Revenue (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Revenue from Contract with Customer, Excluding Assessed Tax	$ 353.9	$ 289.2	$ 959.8	$ 765.2
RTO Revenue	42.1	37.1	134.8	114.0
RTO Capacity Revenue	2.6	2.2	7.0	3.3
Revenues	355.6	294.8	965.4	779.0
Contract with Customer, Asset, before Allowance for Credit Loss	183.3		183.3		$ 158.2
Utility [Member]
RTO Revenue	41.9	37.1	134.5	113.9
RTO Capacity Revenue	2.6	2.2	7.0	3.3
Revenues	353.2	292.7	958.3	772.4
Corporate and Other
RTO Revenue	0.2	0.0	0.3	0.1
RTO Capacity Revenue	0.0	0.0	0.0	0.0
Revenues	3.9	3.6	11.4	11.0
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	(1.5)	(1.5)	(4.3)	(4.4)
Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	2.6	2.5	7.8	7.4
Other non-606 revenue	1.7	5.6	5.6	13.8
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	1.8	5.8	5.7	13.9
Other Revenues [Member] \| Corporate and Other
Revenue from Contract with Customer, Excluding Assessed Tax	2.6	2.5	7.8	7.4
Other non-606 revenue	1.1	1.1	3.3	3.5
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	(1.2)	(1.3)	(3.4)	(3.6)
Wholesale Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	9.5	6.2	30.9	20.1
Wholesale Revenue [Member] \| Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	9.8	6.4	31.8	20.9
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	(0.3)	(0.2)	(0.9)	(0.8)
Retail Revenue [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	297.1	241.2	779.3	620.4
Retail Revenue [Member] \| Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	190.9	153.2	495.9	395.6
Retail Revenue [Member] \| Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	64.6	54.5	173.4	138.3
Retail Revenue [Member] \| Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	26.1	20.7	67.8	54.5
Retail Revenue [Member] \| Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	11.7	9.2	30.6	23.4
Retail Revenue [Member] \| Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	3.8	3.6	11.6	8.6
Retail Revenue [Member] \| Utility [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	297.1	241.2	779.3	620.4
Retail Revenue [Member] \| Utility [Member] \| Residential Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	190.9	153.2	495.9	395.6
Retail Revenue [Member] \| Utility [Member] \| Commercial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	64.6	54.5	173.4	138.3
Retail Revenue [Member] \| Utility [Member] \| Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	26.1	20.7	67.8	54.5
Retail Revenue [Member] \| Utility [Member] \| Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax	11.7	9.2	30.6	23.4
Retail Revenue [Member] \| Utility [Member] \| Other Revenues [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	3.8	3.6	11.6	8.6
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
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
Retail Revenue [Member] \| Adjustments and Eliminations \| Industrial Revenue
Revenue from Contract with Customer, Excluding Assessed Tax			0.0	0.0
Retail Revenue [Member] \| Adjustments and Eliminations \| Governmental Revenue
Revenue from Contract with Customer, Excluding Assessed Tax			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