Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Low [Member]
Commodity Contracts
Electricity physical forward	$ 10.75	$ 8.50
Natural gas financial swaps	2.02	2.06
Fnancial swaps - electricity	19.61	9.98
High [Member]
Commodity Contracts
Electricity physical forward	53.80	84.47
Natural gas financial swaps	3.66	3.70
Fnancial swaps - electricity	34.25	27.36
Weighted Average [Member]
Commodity Contracts
Electricity physical forward	28.67	30.69
Natural gas financial swaps	2.54	2.54
Fnancial swaps - electricity	28.15	19.26
Assets [Member]
Commodity Contracts
Electricity physical forward	0	0
Natural gas financial swaps	0	0
Fnancial swaps - electricity	1,000,000	0
Total commodity contracts	1,000,000	0
Liabilities [Member]
Commodity Contracts
Electricity physical forward	144,000,000	105,000,000
Natural gas financial swaps	14,000,000	14,000,000
Fnancial swaps - electricity	1,000,000	0
Total commodity contracts	$ 159,000,000	$ 119,000,000