Fair Value of FInancial Instruments Fair Value Options Quantitative Disclosure (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	$ 11.97	$ 9.63
Natural gas financial swaps	2.88	3.16
Fnancial swaps - electricity	11.97	9.63
Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	122.72	77.95
Natural gas financial swaps	4.86	4.49
Fnancial swaps - electricity	39.26	46.07
Weighted Average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	37.43	40.18
Natural gas financial swaps	3.41	3.71
Fnancial swaps - electricity	27.88	33.01
Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	0	0
Natural gas financial swaps	0	0
Fnancial swaps - electricity	1,000,000	1,000,000
Total commodity contracts	1,000,000	1,000,000
Liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity physical forward purchase	77,000,000	103,000,000
Natural gas financial swaps	21,000,000	23,000,000
Fnancial swaps - electricity	3,000,000	14,000,000
Total commodity contracts	$ 101,000,000	$ 140,000,000