Commitments And Contingencies (Schedule Of Costs Of Fuel Purchased And Transported As A Percentage Of Total Fuel Costs) (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Marathon Oil Company [Member]
Cost of fuel purchased and transported as a percentage of total fuel costs	72.00%	44.90%	24.10%
Chevron/Unocal/Hilcorp [Member]
Cost of fuel purchased and transported as a percentage of total fuel costs	1.30%	16.10%	26.40%
Municipal Light & Power [Member]
Cost of fuel purchased and transported as a percentage of total fuel costs	0.00%	3.60%	14.20%
ConocoPhillips (COP) [Member]
Cost of fuel purchased and transported as a percentage of total fuel costs	24.20%	31.90%	35.10%
ENSTAR Natural Gas Company [Member]
Cost of fuel purchased and transported as a percentage of total fuel costs	2.20%	1.30%	0.20%
Miscellaneous [Member]
Cost of fuel purchased and transported as a percentage of total fuel costs	0.30%	2.20%	0.00%