Derivative Instruments (Schedule of Concentration Risk Percentage) (Details) - Derivative Credit Risk [Member]	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Concentration Risk, Percentage	100.00%	100.00%
Wells Fargo [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	57.00%	37.00%
Societe Generale [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	27.00%	26.00%
Regions [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	10.00%	8.00%
Union Bank [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	5.00%	4.00%
Credit Suisse [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	0.00%	24.00%
Royal Bank of Canada [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	1.00%	1.00%