Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Low [Member]
Commodity Contracts
Electricity physical forward	$ 11.00	$ 11.97
Natural gas financial swaps	2.06	2.88
Electricity financial futures	21.07	11.97
High [Member]
Commodity Contracts
Electricity physical forward	71.77	122.72
Natural gas financial swaps	3.83	4.86
Electricity financial futures	31.00	39.26
Weighted Average [Member]
Commodity Contracts
Electricity physical forward	29.82	37.43
Natural gas financial swaps	2.56	3.41
Electricity financial futures	27.21	27.88
Assets [Member]
Commodity Contracts
Electricity physical forward	0	0
Natural gas financial swaps	0	0
Electricity financial futures	0	1,000,000
Total commodity contracts	0	1,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forward	117,000,000	77,000,000
Natural gas financial swaps	52,000,000	21,000,000
Electricity financial futures	0	3,000,000
Total commodity contracts	$ 169,000,000	$ 101,000,000