Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Low [Member]
Commodity Contracts
Electricity physical forward	$ 5.45	$ 14.25
Natural gas financial swaps	1.57	1.85
Fnancial swaps - electricity	8.20	8.57
High [Member]
Commodity Contracts
Electricity physical forward	44.76	54.73
Natural gas financial swaps	3.43	4.92
Fnancial swaps - electricity	29.86	33.60
Weighted Average [Member]
Commodity Contracts
Electricity physical forward	31.58	38.18
Natural gas financial swaps	2.14	2.64
Fnancial swaps - electricity	20.42	25.10
Assets [Member]
Commodity Contracts
Electricity physical forward	0	0
Natural gas financial swaps	0	1,000,000
Fnancial swaps - electricity	2,000,000	1,000,000
Total commodity contracts	2,000,000	2,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forward	132,000,000	112,000,000
Natural gas financial swaps	13,000,000	9,000,000
Fnancial swaps - electricity	1,000,000	0
Total commodity contracts	$ 146,000,000	$ 121,000,000