Vogtle Units No. 3 and No. 4 Construction Project - Project Budget and Actual Costs (Details) - Vogtle Units No. 3 & No. 4 - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2021
Project Budget
Project-Level Contingency	$ 90.0	$ 78.0	$ 32.0	$ 112.5
Actual Costs
Totals					$ 17,100.0
Remaining Project Budget
Proceeds from guarantee agreement					1,100.0
Jointly Owned Nuclear Power Plant
Project Budget
Construction Costs					6,140.0
Financing Costs					1,778.0
Total Costs					7,918.0
Project-Level Contingency					90.0
Oglethorpe-Level Contingency					242.0
Total Contingency					332.0
Totals					8,250.0
Actual Costs
Construction Costs					5,342.0
Financing Costs					1,443.0
Total Costs					6,785.0
Project-Level Contingency					0.0
Oglethorpe-Level Contingency					0.0
Total Contingency					0.0
Totals					6,785.0
Remaining Project Budget
Construction Costs					798.0
Financing Costs					335.0
Total Costs					1,133.0
Project-Level Contingency					90.0
Oglethorpe-Level Contingency					242.0
Total Contingency					332.0
Totals					$ 1,465.0