Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 644.1	$ 589.2	$ 1,226.7	$ 1,133.8
Provision for Rate Refund
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0.0	0.6	0.0	2.0
Integrated Market
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	17.1	18.8	32.1	31.5
Transmission
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	42.5	36.1	78.1	71.3
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	7.4	11.1	15.5	22.1
Residential
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	239.0	216.3	460.4	421.8
Commercial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	177.6	152.7	326.4	285.0
Industrial
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	55.2	53.7	108.2	107.0
Oilfield
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	47.6	47.4	97.3	95.5
Public Authority and Street Light
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	57.7	52.5	108.7	97.6
System Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 577.1	$ 522.6	$ 1,101.0	$ 1,006.9