Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Low [Member]
Commodity Contracts
Electricity physical forward	$ 4.25	$ 8.50
Natural gas financial swaps	0.90	2.06
High [Member]
Commodity Contracts
Electricity physical forward	73.32	84.47
Natural gas financial swaps	3.61	3.70
Weighted Average [Member]
Commodity Contracts
Electricity physical forward	29.16	30.69
Natural gas financial swaps	2.46	2.54
Assets [Member]
Commodity Contracts
Electricity physical forward	0	0
Natural gas financial swaps	0	0
Total commodity contracts	0	0
Liabilities [Member]
Commodity Contracts
Electricity physical forward	117,000,000	105,000,000
Natural gas financial swaps	14,000,000	14,000,000
Total commodity contracts	$ 131,000,000	$ 119,000,000