Summary Of Significant Accounting Policies (Schedule Of Depreciation Rates) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Clover [Member]
Segment Reporting Information [Line Items]
Depreciation Rates	1.80%	1.80%	1.80%
North Anna [Member]
Segment Reporting Information [Line Items]
Depreciation Rates	3.00%	3.00%	3.00%
Louisa [Member]
Segment Reporting Information [Line Items]
Depreciation Rates	3.50%	3.50%	3.50%
Marsh Run [Member]
Segment Reporting Information [Line Items]
Depreciation Rates	3.20%	3.20%	3.20%
Rock Springs [Member]
Segment Reporting Information [Line Items]
Depreciation Rates	3.30%	3.30%	3.30%