Fair Value of FInancial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	$ 11.17	$ 12.53
Natural gas financial swaps	1.52	1.39
Fnancial swaps - electricity	8.78	10.57
Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	51.18	59.00
Natural gas financial swaps	4.33	3.73
Fnancial swaps - electricity	58.42	66.32
Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	29.74	36.92
Natural gas financial swaps	2.29	1.90
Fnancial swaps - electricity	43.71	45.11
Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	0	0
Natural gas financial swaps	1,000,000	1,000,000
Fnancial swaps - electricity	4,000,000	7,000,000
Total commodity contracts	5,000,000	8,000,000
Liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	141,000,000	104,000,000
Natural gas financial swaps	1,000,000	0
Fnancial swaps - electricity	0	1,000,000
Total commodity contracts	$ 142,000,000	$ 105,000,000