Contingencies and Regulatory Matters: (Details)						12 Months Ended
	Jan. 01, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 30, 2015 USD ($)	Aug. 20, 2014 item	Jul. 28, 2014 item	Dec. 31, 2015 item	Jun. 30, 2015 USD ($)
Nuclear Construction
Number of electric distribution cooperative members						38
Vogtle Units Number 3 And Number 4
Nuclear Construction
Amount to be paid to the Contractor and capitalized to the project, contingent upon acquisition | $		$ 230,000,000
Payments for Legal Settlements | $	$ 80,000,000		$ 80,000,000
Aggregate Damages Under Initial Complaint And Amended Counterclaim | Vogtle Units Number 3 And Number 4
Nuclear Construction
Contractor's estimated adjustment attributable to the entity | $							$ 470,000,000
Patronage Capital Litigation
Nuclear Construction
Number of defendant members				2	3
Number of excluded members against whom defendant class action is certified					1
Number of electric distribution cooperative members					38
Number of former consumer members					4
Number of members in which the former consumer members filing the lawsuit belonged					4
Percentage of cooperatives total booked patronage capital					30.00%
Number of current consumer members				2
Number of plaintiffs' classes				3
Patronage Capital Litigation | Maximum
Nuclear Construction
Period of revolving schedule to retire the patronage capital of former consumer-members					13 years
Period of revolving schedule to adopt policies to periodically retire the patronage capital of all consumer-members					13 years