Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Low [Member]
Commodity Contracts
Electricity physical forward	$ 15.58	$ 8.50
Natural gas financial swaps	1.84	2.06
Fnancial swaps - electricity	19.29	9.98
High [Member]
Commodity Contracts
Electricity physical forward	41.79	84.47
Natural gas financial swaps	3.23	3.70
Fnancial swaps - electricity	33.75	27.36
Weighted Average [Member]
Commodity Contracts
Electricity physical forward	29.50	30.69
Natural gas financial swaps	2.26	2.54
Fnancial swaps - electricity	26.78	19.26
Assets [Member]
Commodity Contracts
Electricity physical forward	0	0
Natural gas financial swaps	0	0
Fnancial swaps - electricity	0	0
Total commodity contracts	0	0
Liabilities [Member]
Commodity Contracts
Electricity physical forward	139,000,000	105,000,000
Natural gas financial swaps	21,000,000	14,000,000
Fnancial swaps - electricity	0	0
Total commodity contracts	$ 160,000,000	$ 119,000,000