Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Low [Member]
Commodity Contracts
Electricity physical forwards	$ 12.66	$ 12.53
Natural gas financial swaps	1.64	1.39
Financial swaps - electricity	16.50	10.57
High [Member]
Commodity Contracts
Electricity physical forwards	43.21	59.00
Natural gas financial swaps	4.77	3.73
Financial swaps - electricity	56.00	66.32
Weighted Average [Member]
Commodity Contracts
Electricity physical forwards	29.49	36.92
Natural gas financial swaps	2.39	1.90
Financial swaps - electricity	38.63	45.11
Assets [Member]
Commodity Contracts
Electricity physical forwards	0	0
Natural gas financial swaps	10,000,000	1,000,000
Financial swaps - electricity	2,000,000	7,000,000
Total commodity contracts	12,000,000	8,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forwards	144,000,000	104,000,000
Natural gas financial swaps	0	0
Financial swaps - electricity	2,000,000	1,000,000
Total commodity contracts	$ 146,000,000	$ 105,000,000