Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Low [Member]
Commodity Contracts
Electricity physical forward	$ 4.50	$ 9.63
Natural gas financial swaps	3.32	3.16
Electricity financial futures	9.50	9.63
High [Member]
Commodity Contracts
Electricity physical forward	81.20	77.95
Natural gas financial swaps	5.38	4.49
Electricity financial futures	46.62	46.07
Weighted Average [Member]
Commodity Contracts
Electricity physical forward	36.81	40.18
Natural gas financial swaps	3.87	3.71
Electricity financial futures	33.07	33.01
Assets [Member]
Commodity Contracts
Electricity physical forward	0	0
Natural gas financial swaps	1,000,000	0
Electricity financial futures	0	1,000,000
Total commodity contracts	1,000,000	1,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forward	102,000,000	103,000,000
Natural gas financial swaps	17,000,000	23,000,000
Electricity financial futures	13,000,000	14,000,000
Total commodity contracts	$ 132,000,000	$ 140,000,000