Electric plant, construction and related agreements: (Details 2) (USD $)			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Vogtle Units No.3 and No.4 item MW
Construction
Number of Westinghouse AP1000 nuclear generating units			2
Nominally rated generating capacity for each unit			1,100
Ownership interest (as a percent)			30.00%
Revised Estimated proportionate share of construction cost			$ 4,500,000,000
Estimated proportionate share of construction cost			4,200,000,000
Total construction work in progress	$ 2,240,920,000	$ 1,784,264,000	$ 1,689,000,000