Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Low [Member]
Commodity Contracts
Electricity physical forwards	$ 9.04	$ 12.53
Natural gas financial swaps	1.35	1.39
Financial swaps - electricity	9.50	10.57
High [Member]
Commodity Contracts
Electricity physical forwards	43.58	59.00
Natural gas financial swaps	1.83	3.73
Financial swaps - electricity	54.22	66.32
Weighted Average [Member]
Commodity Contracts
Electricity physical forwards	34.25	36.92
Natural gas financial swaps	1.54	1.90
Financial swaps - electricity	38.17	45.11
Assets [Member]
Commodity Contracts
Electricity physical forwards	0	0
Natural gas financial swaps	1,000,000	1,000,000
Financial swaps - electricity	0	7,000,000
Total commodity contracts	1,000,000	8,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forwards	130,000,000	104,000,000
Natural gas financial swaps	1,000,000	0
Financial swaps - electricity	4,000,000	1,000,000
Total commodity contracts	$ 135,000,000	$ 105,000,000