Regulatory Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified											6 Months Ended			6 Months Ended											6 Months Ended											6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Accumulated retirement costs for other obligations	Dec. 31, 2012 Accumulated retirement costs for other obligations	Jun. 30, 2013 Major maintenance sinking fund	Dec. 31, 2012 Major maintenance sinking fund	Jun. 30, 2013 Deferred debt service adder	Dec. 31, 2012 Deferred debt service adder	Jun. 30, 2013 Other regulatory liabilities	Dec. 31, 2012 Other regulatory liabilities	Jun. 30, 2013 Other regulatory liabilities Maximum	Jun. 30, 2013 Premium and loss on reacquired debt	Dec. 31, 2012 Premium and loss on reacquired debt	Jun. 30, 2013 Premium and loss on reacquired debt Maximum	Jun. 30, 2013 Amortization on capital leases	Dec. 31, 2012 Amortization on capital leases	Jun. 30, 2013 Outage costs	Dec. 31, 2012 Outage costs	Jun. 30, 2013 Interest rate swap termination fees	Dec. 31, 2012 Interest rate swap termination fees	Jun. 30, 2013 Asset retirement obligations	Dec. 31, 2012 Asset retirement obligations	Jun. 30, 2013 Depreciation expense	Dec. 31, 2012 Depreciation expense	Jun. 30, 2013 Depreciation expense Plant Vogtle	Jun. 30, 2013 Deferred charges related to Vogtle Units No. 3 and No. 4 training costs Vogtle Units No.3 and No.4	Dec. 31, 2012 Deferred charges related to Vogtle Units No. 3 and No. 4 training costs Vogtle Units No.3 and No.4	Jun. 30, 2013 Interest rate options cost	Dec. 31, 2012 Interest rate options cost	Jun. 30, 2013 Deferral of effects on net margin - Smith Energy Facility Smith	Dec. 31, 2012 Deferral of effects on net margin - Smith Energy Facility Smith	Jun. 30, 2013 Deferral of effects on net margin - Smith Energy Facility Hawk Road	Dec. 31, 2012 Deferral of effects on net margin - Smith Energy Facility Hawk Road	Jun. 30, 2013 Other regulatory assets	Dec. 31, 2012 Other regulatory assets	Jun. 30, 2013 Other regulatory assets Maximum	Jun. 30, 2013 Coal-fired outage costs Minimum	Jun. 30, 2013 Coal-fired outage costs Maximum	Jun. 30, 2013 Nuclear refueling outage costs Minimum	Jun. 30, 2013 Nuclear refueling outage costs Maximum
Regulatory assets and liabilities
Total Regulatory Assets	$ 356,595	$ 352,902										$ 80,534	$ 86,319		$ 22,364	$ 28,670	$ 43,700	$ 30,901	$ 15,331	$ 17,326	$ 7,914	$ 11,382	$ 49,073	$ 49,785		$ 25,668	$ 23,030	$ 58,304	$ 75,716	$ 44,207	$ 21,394			$ 9,500	$ 8,379
Total Regulatory Liabilities	131,819	129,985	25,304	28,846	27,680	30,948	52,349	47,486	5,278	5,592																						21,208	17,113
Net Regulatory Assets	$ 224,776	$ 222,917
Amortization period														30 years																						36 years	18 months	36 months
Operating license expected extension period for Plant Vogtle																									20 years
Operating license, expected extension period, for Plant Vogtle																									40 years
Amortization period											13 years																												18 months	24 months