Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Low [Member]
Commodity Contracts
Natural gas financial swaps	$ 3.22	$ 3.67
Electricity financial swaps	8.91	7.12
Electricity physical forward purchase	8.11
High [Member]
Commodity Contracts
Natural gas financial swaps	4.71	5.21
Electricity financial swaps	48.28	51.72
Electricity physical forward purchase	50.49
Weighted Average [Member]
Commodity Contracts
Natural gas financial swaps	3.87	4.28
Electricity financial swaps	36.23	41.14
Electricity physical forward purchase	32.67
Assets [Member]
Commodity Contracts
Natural gas financial swaps	0	2,000,000
Electricity financial swaps	0	0
Electricity physical forward purchase	0
Total commodity contracts	0	2,000,000
Liabilities [Member]
Commodity Contracts
Natural gas financial swaps	25,000,000	8,000,000
Electricity financial swaps	13,000,000	10,000,000
Electricity physical forward purchase	26,000,000
Total commodity contracts	$ 64,000,000	$ 18,000,000