Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Low [Member]
Commodity Contracts
Electricity physical forward	$ 10.97	$ 11.97
Natural gas financial swaps	2.48	2.88
Electricity financial futures	10.97	11.97
High [Member]
Commodity Contracts
Electricity physical forward	95.47	122.72
Natural gas financial swaps	4.36	4.86
Electricity financial futures	34.63	39.26
Weighted Average [Member]
Commodity Contracts
Electricity physical forward	33.11	37.43
Natural gas financial swaps	2.94	3.41
Electricity financial futures	22.82	27.88
Assets [Member]
Commodity Contracts
Electricity physical forward	0	0
Natural gas financial swaps	0	0
Electricity financial futures	2,000,000	1,000,000
Total commodity contracts	2,000,000	1,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forward	112,000,000	77,000,000
Natural gas financial swaps	36,000,000	21,000,000
Electricity financial futures	2,000,000	3,000,000
Total commodity contracts	$ 150,000,000	$ 101,000,000