Schedule of Power Cost Adjustment Mechanism (Details) - Subsidiaries [Member] $ in Millions			6 Months Ended		12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability, Interest			$ 0.7	$ 1.1
Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability, Amount			30.5	48.8	$ 67.2
Customer's share [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability, Amount			$ 6.7	$ 19.5	36.0
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 1 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability			0
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 2 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability			0.50
Customer's share [Member] | Range 3 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability			0.90
Customer's share [Member] | Range 3 [Member] | Under-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					31.2
Companys share [Member] | Range 1 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability			1
Companys share [Member] | Range 1 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability			1
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 2 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability			0.50
Companys share [Member] | Range 3 [Member] | Over-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability			0.10
Companys share [Member] | Range 3 [Member] | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability			0.10
Customer's share plus interest | Under-collection [Member]
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability, Amount	$ 41.7	$ 4.7			37.0
Customer's share plus interest | Maximum Power
Regulatory Assets and Liabiliaties [Line Items]
Annual Power Cost Variability, Amount					$ 20.0