Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Low [Member]
Commodity Contracts
Electricity physical forward	$ 12.97	$ 11.97
Natural gas financial swaps	2.40	2.88
Electricity financial futures	21.35	11.97
High [Member]
Commodity Contracts
Electricity physical forward	66.27	122.72
Natural gas financial swaps	4.33	4.86
Electricity financial futures	37.90	39.26
Weighted Average [Member]
Commodity Contracts
Electricity physical forward	31.43	37.43
Natural gas financial swaps	2.90	3.41
Electricity financial futures	30.56	27.88
Assets [Member]
Commodity Contracts
Electricity physical forward	0	0
Natural gas financial swaps	0	0
Electricity financial futures	1,000,000	1,000,000
Total commodity contracts	1,000,000	1,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forward	131,000,000	77,000,000
Natural gas financial swaps	37,000,000	21,000,000
Electricity financial futures	1,000,000	3,000,000
Total commodity contracts	$ 169,000,000	$ 101,000,000