Schedule of Power Cost Adjustment Mechanism (Details) - Subsidiaries [Member] $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability, Interest		$ 1.1	$ 0.2
Customer's share [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability, Amount		19.5	17.3
Customer's share [Member] | Range 1 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0
Customer's share [Member] | Range 1 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0
Customer's share [Member] | Range 2 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0.50
Customer's share [Member] | Range 2 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0.65
Customer's share [Member] | Range 3 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0.90
Customer's share [Member] | Range 3 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0.90
Companys share [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability, Amount		$ 48.8	$ 46.4
Companys share [Member] | Range 1 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	1
Companys share [Member] | Range 1 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	1
Companys share [Member] | Range 2 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0.50
Companys share [Member] | Range 2 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0.35
Companys share [Member] | Range 3 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0.10
Companys share [Member] | Range 3 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability	0.10