Assets and Liabilities with Recurring Fair Value Measurements Quantitative Information about Level 3 Fair Value Measurements (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Physical Power [Member]
Quantitative Information about Level 3 fair Value Measurements [Line Items]
Fair Value Inputs Quantitative Information Power	$ 7,000,000	$ 11,000,000
Power Congestion Products [Member]
Quantitative Information about Level 3 fair Value Measurements [Line Items]
Fair Value Inputs Quantitative Information Power	7,000,000
Minimum [Member] | Physical Power [Member]
Quantitative Information about Level 3 fair Value Measurements [Line Items]
Fair Value Inputs Quantitative Information Power	28.92	23.75
Minimum [Member] | Power Congestion Products [Member]
Quantitative Information about Level 3 fair Value Measurements [Line Items]
Fair Value Inputs Quantitative Information Power	(8.79)
Maximum [Member] | Physical Power [Member]
Quantitative Information about Level 3 fair Value Measurements [Line Items]
Fair Value Inputs Quantitative Information Power	53.15	53.82
Maximum [Member] | Power Congestion Products [Member]
Quantitative Information about Level 3 fair Value Measurements [Line Items]
Fair Value Inputs Quantitative Information Power	$ 11.53