Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Low [Member]
Commodity Contracts
Electricity physical forwards	$ 13.63	$ 14.60
Natural gas financial swaps	1.03	0.95
Financial swaps - electricity	24.79
High [Member]
Commodity Contracts
Electricity physical forwards	78.80	69.00
Natural gas financial swaps	3.67	4.64
Financial swaps - electricity	60.25
Weighted Average [Member]
Commodity Contracts
Electricity physical forwards	51.43	45.00
Natural gas financial swaps	1.67	1.82
Financial swaps - electricity	37.17
Assets [Member]
Commodity Contracts
Electricity physical forwards	1,000,000	3,000,000
Natural gas financial swaps	1,000,000	0
Financial swaps - electricity	0
Total commodity contracts	2,000,000	3,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forwards	68,000,000	84,000,000
Natural gas financial swaps	5,000,000	7,000,000
Financial swaps - electricity	1,000,000
Total commodity contracts	$ 74,000,000	$ 91,000,000