Fair Value of FInancial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	$ 12.53	$ 14.60
Natural gas financial swaps	1.39	0.95
Fnancial swaps - electricity	10.57	20.75
Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	59.00	69.00
Natural gas financial swaps	3.73	4.64
Fnancial swaps - electricity	66.32	35.46
Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	36.92	45.00
Natural gas financial swaps	1.90	1.82
Fnancial swaps - electricity	45.11	28.63
Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	0	3,000,000
Natural gas financial swaps	1,000,000	0
Fnancial swaps - electricity	7,000,000	0
Total commodity contracts	8,000,000	3,000,000
Liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	104,000,000	84,000,000
Natural gas financial swaps	0	7,000,000
Fnancial swaps - electricity	1,000,000	0
Total commodity contracts	$ 105,000,000	$ 91,000,000